diff --git a/app/socketio/chat_handlers.py b/app/socketio/chat_handlers.py
new file mode 100644
index 0000000..59a4c41
--- /dev/null
+++ b/app/socketio/chat_handlers.py
@@ -0,0 +1,391 @@
+"""
+聊天 WebSocket 事件处理器
+实现智队机器人的聊天功能
+"""
+from flask_socketio import emit, join_room, leave_room, rooms
+from flask import request
+from datetime import datetime
+from typing import Optional, Dict, Any
+
+from app.extensions import db, redis_client
+from app.models import User, Session, Message, Bot, Agent, Connection
+from app.services.bot_service import BotService
+from app.services.session_service import SessionService
+
+
+class ChatConnectionManager:
+    """聊天连接管理器"""
+    
+    def __init__(self):
+        # socket_id -> {user_id, current_session_id}
+        self.connections: Dict[str, Dict[str, Any]] = {}
+    
+    def add_connection(self, socket_id: str, user_id: str):
+        """添加连接"""
+        self.connections[socket_id] = {
+            'user_id': user_id,
+            'current_session_id': None,
+            'connected_at': datetime.utcnow()
+        }
+    
+    def set_current_session(self, socket_id: str, session_id: Optional[str]):
+        """设置当前会话"""
+        if socket_id in self.connections:
+            self.connections[socket_id]['current_session_id'] = session_id
+    
+    def get_user_id(self, socket_id: str) -> Optional[str]:
+        """获取用户 ID"""
+        return self.connections.get(socket_id, {}).get('user_id')
+    
+    def get_current_session(self, socket_id: str) -> Optional[str]:
+        """获取当前会话 ID"""
+        return self.connections.get(socket_id, {}).get('current_session_id')
+    
+    def remove_connection(self, socket_id: str):
+        """移除连接"""
+        if socket_id in self.connections:
+            del self.connections[socket_id]
+
+
+# 全局聊天连接管理器
+chat_manager = ChatConnectionManager()
+
+
+def get_user_from_socket(socket_id: str) -> Optional[User]:
+    """从 socket_id 获取用户"""
+    user_id = chat_manager.get_user_id(socket_id)
+    if user_id:
+        return User.query.get(user_id)
+    return None
+
+
+def emit_chat_error(message: str, code: str = 'CHAT_ERROR', session_id: Optional[str] = None):
+    """发送聊天错误"""
+    error_data = {
+        'code': code,
+        'message': message
+    }
+    if session_id:
+        error_data['session_id'] = session_id
+    emit('chat_error', error_data)
+
+
+def register_chat_handlers(socketio):
+    """注册聊天事件处理器"""
+    
+    # ==================== 创建会话 ====================
+    @socketio.on('chat.send.create')
+    def handle_chat_create(data):
+        """
+        创建聊天会话
+        
+        参数:
+            - bot_id: str - 机器人 ID（必填）
+            - title: str - 会话标题（可选）
+        """
+        sid = request.sid
+        user = get_user_from_socket(sid)
+        
+        if not user:
+            return emit_chat_error('User not authenticated', 'AUTH_REQUIRED')
+        
+        bot_id = data.get('bot_id')
+        if not bot_id:
+            return emit_chat_error('bot_id is required', 'MISSING_BOT_ID')
+        
+        # 获取 Bot
+        bot = BotService.get_bot_by_id(bot_id)
+        if not bot:
+            return emit_chat_error('Bot not found', 'BOT_NOT_FOUND')
+        
+        # 检查权限
+        if not BotService.check_permission(user, bot, 'use'):
+            return emit_chat_error('Permission denied', 'PERMISSION_DENIED')
+        
+        # 检查 Bot 是否绑定了 Agent
+        if not bot.agent_id:
+            return emit_chat_error('Bot has no agent bound', 'NO_AGENT_BOUND')
+        
+        # 检查 Agent 是否在线
+        agent = Agent.query.get(bot.agent_id)
+        if not agent or agent.status != 'online':
+            return emit_chat_error('Agent is offline', 'AGENT_OFFLINE')
+        
+        # 创建会话
+        title = data.get('title', f'Chat with {bot.display_name or bot.name}')
+        session = Session(
+            user_id=user.id,
+            bot_id=bot.id,
+            primary_agent_id=agent.id,
+            title=title,
+            channel_type='pit-bot',
+            status='active',
+            created_at=datetime.utcnow(),
+            last_active_at=datetime.utcnow()
+        )
+        db.session.add(session)
+        db.session.commit()
+        
+        # 加入房间
+        join_room(session.id)
+        chat_manager.set_current_session(sid, session.id)
+        
+        # 返回创建结果
+        emit('chat.created', {
+            'session_id': session.id,
+            'bot': bot.to_dict(),
+            'agent': {
+                'id': agent.id,
+                'name': agent.name,
+                'display_name': agent.display_name
+            },
+            'title': title,
+            'created_at': session.created_at.isoformat()
+        })
+    
+    # ==================== 加入会话 ====================
+    @socketio.on('chat.send.join')
+    def handle_chat_join(data):
+        """
+        加入会话
+        
+        参数:
+            - session_id: str - 会话 ID
+        """
+        sid = request.sid
+        user = get_user_from_socket(sid)
+        
+        if not user:
+            return emit_chat_error('User not authenticated', 'AUTH_REQUIRED')
+        
+        session_id = data.get('session_id')
+        if not session_id:
+            return emit_chat_error('session_id is required', 'MISSING_SESSION_ID')
+        
+        # 获取会话
+        session = Session.query.get(session_id)
+        if not session:
+            return emit_chat_error('Session not found', 'SESSION_NOT_FOUND', session_id)
+        
+        # 检查权限
+        if session.user_id != user.id:
+            return emit_chat_error('Permission denied', 'PERMISSION_DENIED', session_id)
+        
+        # 获取 Bot 信息
+        bot = None
+        if session.bot_id:
+            bot = BotService.get_bot_by_id(session.bot_id)
+        
+        # 获取历史消息
+        messages = Message.query.filter_by(session_id=session_id)\
+            .order_by(Message.created_at.desc())\
+            .limit(50)\
+            .all()
+        
+        # 加入房间
+        join_room(session_id)
+        chat_manager.set_current_session(sid, session_id)
+        
+        # 返回加入结果
+        emit('chat.joined', {
+            'session_id': session_id,
+            'bot': bot.to_dict() if bot else None,
+            'messages': [m.to_dict() for m in reversed(messages)],
+            'message_count': len(messages)
+        })
+    
+    # ==================== 离开会话 ====================
+    @socketio.on('chat.send.leave')
+    def handle_chat_leave(data):
+        """
+        离开会话
+        
+        参数:
+            - session_id: str - 会话 ID
+        """
+        sid = request.sid
+        session_id = data.get('session_id')
+        
+        if not session_id:
+            return emit_chat_error('session_id is required', 'MISSING_SESSION_ID')
+        
+        # 离开房间
+        leave_room(session_id)
+        chat_manager.set_current_session(sid, None)
+        
+        emit('chat.left', {'session_id': session_id})
+    
+    # ==================== 发送消息 ====================
+    @socketio.on('chat.send.message')
+    def handle_chat_message(data):
+        """
+        发送消息
+        
+        参数:
+            - session_id: str - 会话 ID
+            - content: str - 消息内容
+            - reply_to: str - 回复的消息 ID（可选）
+        """
+        sid = request.sid
+        user = get_user_from_socket(sid)
+        
+        if not user:
+            return emit_chat_error('User not authenticated', 'AUTH_REQUIRED')
+        
+        session_id = data.get('session_id')
+        content = data.get('content')
+        reply_to = data.get('reply_to')
+        
+        if not session_id:
+            return emit_chat_error('session_id is required', 'MISSING_SESSION_ID')
+        
+        if not content or not content.strip():
+            return emit_chat_error('content is required', 'MISSING_CONTENT', session_id)
+        
+        # 获取会话
+        session = Session.query.get(session_id)
+        if not session:
+            return emit_chat_error('Session not found', 'SESSION_NOT_FOUND', session_id)
+        
+        # 检查权限
+        if session.user_id != user.id:
+            return emit_chat_error('Permission denied', 'PERMISSION_DENIED', session_id)
+        
+        # 获取 Bot 信息
+        bot = None
+        sender_name = user.nickname or user.username
+        if session.bot_id:
+            bot = BotService.get_bot_by_id(session.bot_id)
+        
+        # 创建用户消息
+        message = Message(
+            session_id=session_id,
+            sender_type='user',
+            sender_id=user.id,
+            sender_name=sender_name,
+            bot_id=session.bot_id,
+            message_type='text',
+            content=content.strip(),
+            content_type='markdown',
+            reply_to=reply_to,
+            status='sent',
+            ack_status='pending',
+            created_at=datetime.utcnow()
+        )
+        db.session.add(message)
+        
+        # 更新会话
+        session.message_count += 1
+        session.last_active_at = datetime.utcnow()
+        session.updated_at = datetime.utcnow()
+        
+        db.session.commit()
+        
+        # 广播消息到房间（用户端）
+        emit('chat.message', {
+            'message_id': message.id,
+            'session_id': session_id,
+            'sender_type': 'user',
+            'sender_id': user.id,
+            'sender_name': sender_name,
+            'bot_id': session.bot_id,
+            'content': content.strip(),
+            'content_type': 'markdown',
+            'reply_to': reply_to,
+            'timestamp': message.created_at.isoformat()
+        }, room=session_id)
+        
+        # TODO: 转发消息给 Agent（通过 PIT Channel 协议）
+        # 这里需要实现将消息转发给绑定的 Agent
+        # 使用 session.primary_agent_id 获取 Agent
+        # 然后通过 Agent 的 socket_id 发送消息
+    
+    # ==================== 正在输入 ====================
+    @socketio.on('chat.send.typing')
+    def handle_chat_typing(data):
+        """
+        正在输入状态
+        
+        参数:
+            - session_id: str - 会话 ID
+            - is_typing: bool - 是否正在输入
+        """
+        sid = request.sid
+        user = get_user_from_socket(sid)
+        
+        if not user:
+            return
+        
+        session_id = data.get('session_id')
+        is_typing = data.get('is_typing', False)
+        
+        if not session_id:
+            return
+        
+        # 广播输入状态到房间（除了发送者）
+        emit('chat.typing', {
+            'session_id': session_id,
+            'user_id': user.id,
+            'user_name': user.nickname or user.username,
+            'is_typing': is_typing
+        }, room=session_id, include_self=False)
+    
+    # ==================== 消息已读 ====================
+    @socketio.on('chat.send.read')
+    def handle_chat_read(data):
+        """
+        标记消息已读
+        
+        参数:
+            - session_id: str - 会话 ID
+            - message_ids: list - 消息 ID 列表
+        """
+        sid = request.sid
+        user = get_user_from_socket(sid)
+        
+        if not user:
+            return emit_chat_error('User not authenticated', 'AUTH_REQUIRED')
+        
+        session_id = data.get('session_id')
+        message_ids = data.get('message_ids', [])
+        
+        if not session_id:
+            return emit_chat_error('session_id is required', 'MISSING_SESSION_ID')
+        
+        # 更新消息状态
+        for msg_id in message_ids:
+            message = Message.query.get(msg_id)
+            if message and message.session_id == session_id:
+                message.status = 'read'
+        
+        # 更新会话未读数
+        session = Session.query.get(session_id)
+        if session:
+            session.unread_count = 0
+        
+        db.session.commit()
+        
+        # 返回已读确认
+        emit('chat.read', {
+            'session_id': session_id,
+            'message_ids': message_ids
+        })
+    
+    # ==================== 关闭会话 ====================
+    def close_chat_session(session_id: str, reason: str = 'closed'):
+        """关闭聊天会话（内部方法）"""
+        session = Session.query.get(session_id)
+        if session:
+            session.status = 'closed'
+            session.updated_at = datetime.utcnow()
+            db.session.commit()
+            
+            # 通知房间内的所有用户
+            emit('chat.closed', {
+                'session_id': session_id,
+                'reason': reason
+            }, room=session_id)
+
+
+# 导出注册函数
+__all__ = ['register_chat_handlers', 'chat_manager']
diff --git a/app/socketio/handlers.py b/app/socketio/handlers.py
index 29db808..2b11a51 100644
--- a/app/socketio/handlers.py
+++ b/app/socketio/handlers.py
@@ -20,6 +20,7 @@ connection_manager = ConnectionManager()
 def register_handlers(socketio):
     """注册 Socket.IO 事件处理器"""
     
+    # ==================== 连接事件 ====================
     @socketio.on('connect')
     def handle_connect():
         """客户端连接"""
@@ -38,10 +39,13 @@ def register_handlers(socketio):
         if sid in connection_manager.socket_sessions:
             del connection_manager.socket_sessions[sid]
     
+    # ==================== 认证事件 ====================
     @socketio.on('auth')
     def handle_auth(data):
         """处理认证"""
         from flask import request
+        from app.models import User
+        
         sid = request.sid
         
         token = data.get('token')
@@ -71,11 +75,13 @@ def register_handlers(socketio):
         except Exception as e:
             emit('auth_error', {'code': 'INVALID_TOKEN', 'message': str(e)})
     
+    # ==================== 心跳事件 ====================
     @socketio.on('ping')
     def handle_ping(data):
         """心跳响应"""
         emit('pong', {'timestamp': datetime.utcnow().timestamp()})
     
+    # ==================== 会话事件 ====================
     @socketio.on('session.create')
     def handle_session_create(data):
         """创建会话"""
@@ -124,6 +130,7 @@ def register_handlers(socketio):
                 'participants': [session.user_id, session.primary_agent_id]
             })
     
+    # ==================== 消息事件 ====================
     @socketio.on('message.send')
     def handle_message_send(data):
         """发送消息"""
@@ -180,3 +187,7 @@ def register_handlers(socketio):
             db.session.commit()
         
         emit('message.acked', {'message_id': message_id, 'status': status})
+    
+    # ==================== 聊天事件 (Step 4) ====================
+    from app.socketio.chat_handlers import register_chat_handlers
+    register_chat_handlers(socketio)