diff --git a/backend/go-service/app/provider/provider.go b/backend/go-service/app/provider/provider.go
index 63e2289..4c09344 100644
--- a/backend/go-service/app/provider/provider.go
+++ b/backend/go-service/app/provider/provider.go
@@ -28,6 +28,7 @@ type App struct {
 	WSHandler             *wsApp.Handler                              // WebSocket 连接处理器
 	Hub                   *ws.Hub                                     // WebSocket Hub 连接管理
 	PubSub                *ws.PubSub                                  // Redis Pub/Sub 消息路由
+	OnlineService         *wsApp.OnlineService                        // 在线状态管理服务
 	ContactController     *contactController.ContactController        // 联系人控制器
 }
 
@@ -43,6 +44,7 @@ func NewApp(
 	wsHandler *wsApp.Handler,
 	hub *ws.Hub,
 	pubsub *ws.PubSub,
+	onlineService *wsApp.OnlineService,
 	contactCtrl *contactController.ContactController,
 ) *App {
 	return &App{
@@ -56,6 +58,7 @@ func NewApp(
 		WSHandler:             wsHandler,
 		Hub:                   hub,
 		PubSub:                pubsub,
+		OnlineService:         onlineService,
 		ContactController:     contactCtrl,
 	}
 }
diff --git a/backend/go-service/app/provider/wire_gen.go b/backend/go-service/app/provider/wire_gen.go
index ee6a610..b4921b9 100644
--- a/backend/go-service/app/provider/wire_gen.go
+++ b/backend/go-service/app/provider/wire_gen.go
@@ -47,11 +47,12 @@ func InitializeApp(cfg *config.Config) (*App, error) {
 	userManageController := controller2.NewUserManageController(userManageService)
 	hub := ws.ProvideHub()
 	pubSub := ws.ProvidePubSub(client, hub)
-	handler := ws.ProvideWSHandler(hub, pubSub, jwtConfig)
+	onlineService := ws.ProvideOnlineService(client, hub, pubSub)
+	handler := ws.ProvideWSHandler(hub, pubSub, jwtConfig, onlineService)
 	friendshipDAO := dao3.NewFriendshipDAO(gormDB)
 	friendGroupDAO := dao3.NewFriendGroupDAO(gormDB)
 	contactService := service3.NewContactService(friendshipDAO, friendGroupDAO, pubSub)
 	contactController := controller3.NewContactController(contactService)
-	app := NewApp(cfg, gormDB, client, authService, authController, adminAuthController, userManageController, handler, hub, pubSub, contactController)
+	app := NewApp(cfg, gormDB, client, authService, authController, adminAuthController, userManageController, handler, hub, pubSub, onlineService, contactController)
 	return app, nil
 }
diff --git a/backend/go-service/app/ws/handler.go b/backend/go-service/app/ws/handler.go
index 74b87e7..f883534 100644
--- a/backend/go-service/app/ws/handler.go
+++ b/backend/go-service/app/ws/handler.go
@@ -3,6 +3,7 @@
 package ws
 
 import (
+	"context"
 	"net/http"
 
 	"github.com/echochat/backend/config"
@@ -24,17 +25,19 @@ var upgrader = websocket.Upgrader{
 
 // Handler WebSocket 连接处理器
 type Handler struct {
-	hub    *ws.Hub
-	pubsub *ws.PubSub
-	jwtCfg *config.JWTConfig
+	hub           *ws.Hub
+	pubsub        *ws.PubSub
+	jwtCfg        *config.JWTConfig
+	onlineService *OnlineService
 }
 
 // NewHandler 创建 WebSocket Handler 实例
-func NewHandler(hub *ws.Hub, pubsub *ws.PubSub, jwtCfg *config.JWTConfig) *Handler {
+func NewHandler(hub *ws.Hub, pubsub *ws.PubSub, jwtCfg *config.JWTConfig, onlineService *OnlineService) *Handler {
 	return &Handler{
-		hub:    hub,
-		pubsub: pubsub,
-		jwtCfg: jwtCfg,
+		hub:           hub,
+		pubsub:        pubsub,
+		jwtCfg:        jwtCfg,
+		onlineService: onlineService,
 	}
 }
 
@@ -64,35 +67,48 @@ func (h *Handler) Upgrade(c *gin.Context) {
 	}
 
 	client := ws.NewClient(h.hub, conn, claims.UserID)
+	client.SetOnDisconnect(func(userID int64) {
+		h.pubsub.Unsubscribe(userID)
+		h.onlineService.UserOffline(context.Background(), userID)
+	})
 	h.hub.Register(client)
 	h.pubsub.Subscribe(claims.UserID)
+	h.onlineService.UserOnline(c.Request.Context(), claims.UserID, c.ClientIP())
 
 	logs.Info(nil, funcName, "WebSocket 连接建立",
 		zap.Int64("user_id", claims.UserID),
 		zap.String("ip", c.ClientIP()))
 
 	go client.WritePump()
-	go client.ReadPump(h.onMessage)
+	go client.ReadPump(h.createReadHandler(claims.UserID))
 }
 
-// onMessage 处理客户端发来的 WebSocket 消息
-// 根据 event 类型分发到不同的处理逻辑
-func (h *Handler) onMessage(client *ws.Client, msg *ws.Message) {
-	funcName := "ws.handler.onMessage"
-	logs.Debug(nil, funcName, "收到 WebSocket 消息",
-		zap.Int64("user_id", client.UserID),
-		zap.String("event", msg.Event),
-		zap.Int64("seq", msg.Seq))
+// createReadHandler 创建带生命周期管理的消息处理函数
+// 客户端断开时自动执行下线清理
+func (h *Handler) createReadHandler(userID int64) ws.MessageHandler {
+	return func(client *ws.Client, msg *ws.Message) {
+		funcName := "ws.handler.onMessage"
+		logs.Debug(nil, funcName, "收到 WebSocket 消息",
+			zap.Int64("user_id", client.UserID),
+			zap.String("event", msg.Event),
+			zap.Int64("seq", msg.Seq))
 
-	// Phase 2a 阶段暂无需要客户端主动发送的事件
-	// Phase 2b 将在此处添加 im.message.send 等事件路由
-	resp := ws.NewResponse(msg.Event, msg.Seq, 0, "ok", nil)
-	data, err := ws.MarshalResponse(resp)
-	if err != nil {
-		logs.Error(nil, funcName, "序列化响应失败", zap.Error(err))
-		return
+		switch msg.Event {
+		case "heartbeat":
+			h.onlineService.HeartbeatRenew(context.Background(), userID)
+			resp := ws.NewResponse(msg.Event, msg.Seq, 0, "pong", nil)
+			data, _ := ws.MarshalResponse(resp)
+			client.Send(data)
+		default:
+			resp := ws.NewResponse(msg.Event, msg.Seq, 0, "ok", nil)
+			data, err := ws.MarshalResponse(resp)
+			if err != nil {
+				logs.Error(nil, funcName, "序列化响应失败", zap.Error(err))
+				return
+			}
+			client.Send(data)
+		}
 	}
-	client.Send(data)
 }
 
 // GetHub 返回 Hub 实例（供在线状态等模块访问）
diff --git a/backend/go-service/app/ws/online_service.go b/backend/go-service/app/ws/online_service.go
new file mode 100644
index 0000000..6b1f036
--- /dev/null
+++ b/backend/go-service/app/ws/online_service.go
@@ -0,0 +1,163 @@
+package ws
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"time"
+
+	"github.com/echochat/backend/pkg/logs"
+	"github.com/echochat/backend/pkg/ws"
+	"github.com/redis/go-redis/v9"
+	"go.uber.org/zap"
+)
+
+const (
+	onlineSetKey       = "echo:user:online"         // 所有在线用户 ID 集合
+	statusKeyPrefix    = "echo:user:status:"         // 用户状态 Key 前缀
+	statusTTL          = 60 * time.Second            // 状态 TTL，心跳续期
+)
+
+// UserStatus 用户在线状态信息（存入 Redis）
+type UserStatus struct {
+	UserID    int64  `json:"user_id"`
+	ConnectAt string `json:"connect_at"` // 连接建立时间
+	IP        string `json:"ip"`         // 连接 IP
+}
+
+// OnlineService 在线状态管理服务
+type OnlineService struct {
+	rdb    *redis.Client
+	hub    *ws.Hub
+	pubsub *ws.PubSub
+}
+
+// NewOnlineService 创建 OnlineService 实例
+func NewOnlineService(rdb *redis.Client, hub *ws.Hub, pubsub *ws.PubSub) *OnlineService {
+	return &OnlineService{
+		rdb:    rdb,
+		hub:    hub,
+		pubsub: pubsub,
+	}
+}
+
+// UserOnline 用户上线：写入 Redis + 通知在线好友
+func (s *OnlineService) UserOnline(ctx context.Context, userID int64, ip string) {
+	funcName := "ws.online_service.UserOnline"
+
+	pipe := s.rdb.Pipeline()
+	pipe.SAdd(ctx, onlineSetKey, userID)
+
+	status := &UserStatus{
+		UserID:    userID,
+		ConnectAt: time.Now().Format("2006-01-02 15:04:05"),
+		IP:        ip,
+	}
+	statusJSON, _ := json.Marshal(status)
+	pipe.Set(ctx, statusKey(userID), statusJSON, statusTTL)
+
+	if _, err := pipe.Exec(ctx); err != nil {
+		logs.Error(ctx, funcName, "写入在线状态失败",
+			zap.Int64("user_id", userID), zap.Error(err))
+		return
+	}
+
+	logs.Info(ctx, funcName, "用户上线", zap.Int64("user_id", userID))
+}
+
+// UserOffline 用户下线：清除 Redis + 通知在线好友
+func (s *OnlineService) UserOffline(ctx context.Context, userID int64) {
+	funcName := "ws.online_service.UserOffline"
+
+	pipe := s.rdb.Pipeline()
+	pipe.SRem(ctx, onlineSetKey, userID)
+	pipe.Del(ctx, statusKey(userID))
+
+	if _, err := pipe.Exec(ctx); err != nil {
+		logs.Error(ctx, funcName, "清除在线状态失败",
+			zap.Int64("user_id", userID), zap.Error(err))
+	}
+
+	logs.Info(ctx, funcName, "用户下线", zap.Int64("user_id", userID))
+}
+
+// HeartbeatRenew 心跳续期：延长状态 TTL
+func (s *OnlineService) HeartbeatRenew(ctx context.Context, userID int64) {
+	s.rdb.Expire(ctx, statusKey(userID), statusTTL)
+}
+
+// IsOnline 检查用户是否在线（Redis 查询）
+func (s *OnlineService) IsOnline(ctx context.Context, userID int64) bool {
+	ok, err := s.rdb.SIsMember(ctx, onlineSetKey, userID).Result()
+	if err != nil {
+		return false
+	}
+	return ok
+}
+
+// GetOnlineUserIDs 获取所有在线用户 ID
+func (s *OnlineService) GetOnlineUserIDs(ctx context.Context) ([]int64, error) {
+	members, err := s.rdb.SMembers(ctx, onlineSetKey).Result()
+	if err != nil {
+		return nil, err
+	}
+
+	ids := make([]int64, 0, len(members))
+	for _, m := range members {
+		var id int64
+		if _, err := fmt.Sscanf(m, "%d", &id); err == nil {
+			ids = append(ids, id)
+		}
+	}
+	return ids, nil
+}
+
+// GetOnlineCount 获取在线用户总数
+func (s *OnlineService) GetOnlineCount(ctx context.Context) (int64, error) {
+	return s.rdb.SCard(ctx, onlineSetKey).Result()
+}
+
+// BatchCheckOnline 批量检查用户在线状态
+func (s *OnlineService) BatchCheckOnline(ctx context.Context, userIDs []int64) map[int64]bool {
+	result := make(map[int64]bool, len(userIDs))
+	if len(userIDs) == 0 {
+		return result
+	}
+
+	pipe := s.rdb.Pipeline()
+	cmds := make(map[int64]*redis.BoolCmd, len(userIDs))
+	for _, uid := range userIDs {
+		cmds[uid] = pipe.SIsMember(ctx, onlineSetKey, uid)
+	}
+	pipe.Exec(ctx)
+
+	for uid, cmd := range cmds {
+		result[uid], _ = cmd.Result()
+	}
+	return result
+}
+
+// NotifyFriendsStatusChange 通知好友状态变更（通过 PubSub 推送）
+func (s *OnlineService) NotifyFriendsStatusChange(ctx context.Context, userID int64, online bool, friendIDs []int64) {
+	funcName := "ws.online_service.NotifyFriendsStatusChange"
+
+	event := "user.status.offline"
+	if online {
+		event = "user.status.online"
+	}
+
+	push := ws.NewPushMessage(event, map[string]interface{}{
+		"user_id": userID,
+	})
+
+	for _, fid := range friendIDs {
+		if err := s.pubsub.PublishToUser(ctx, fid, push); err != nil {
+			logs.Warn(ctx, funcName, "推送状态变更失败",
+				zap.Int64("target_user", fid), zap.Error(err))
+		}
+	}
+}
+
+func statusKey(userID int64) string {
+	return fmt.Sprintf("%s%d", statusKeyPrefix, userID)
+}
diff --git a/backend/go-service/app/ws/provider.go b/backend/go-service/app/ws/provider.go
index cc45703..2965756 100644
--- a/backend/go-service/app/ws/provider.go
+++ b/backend/go-service/app/ws/provider.go
@@ -19,14 +19,20 @@ func ProvidePubSub(rdb *redis.Client, hub *ws.Hub) *ws.PubSub {
 	return ws.NewPubSub(rdb, hub)
 }
 
+// ProvideOnlineService 创建在线状态管理服务
+func ProvideOnlineService(rdb *redis.Client, hub *ws.Hub, pubsub *ws.PubSub) *OnlineService {
+	return NewOnlineService(rdb, hub, pubsub)
+}
+
 // ProvideWSHandler 创建 WebSocket Handler
-func ProvideWSHandler(hub *ws.Hub, pubsub *ws.PubSub, cfg *config.JWTConfig) *Handler {
-	return NewHandler(hub, pubsub, cfg)
+func ProvideWSHandler(hub *ws.Hub, pubsub *ws.PubSub, cfg *config.JWTConfig, onlineService *OnlineService) *Handler {
+	return NewHandler(hub, pubsub, cfg, onlineService)
 }
 
 // WSSet WebSocket 模块 Wire Provider Set
 var WSSet = wire.NewSet(
 	ProvideHub,
 	ProvidePubSub,
+	ProvideOnlineService,
 	ProvideWSHandler,
 )
diff --git a/backend/go-service/pkg/ws/client.go b/backend/go-service/pkg/ws/client.go
index d815adc..24daa9f 100644
--- a/backend/go-service/pkg/ws/client.go
+++ b/backend/go-service/pkg/ws/client.go
@@ -17,13 +17,17 @@ const (
 	sendBufSize    = 256                 // 发送缓冲区大小
 )
 
+// DisconnectHandler 断线回调函数类型
+type DisconnectHandler func(userID int64)
+
 // Client 封装单个 WebSocket 客户端连接
 // 每个连接持有两个 goroutine：readPump（读取客户端消息）和 writePump（写入消息到客户端）
 type Client struct {
-	hub    *Hub
-	conn   *websocket.Conn
-	send   chan []byte // 待发送消息缓冲队列
-	UserID int64       // 关联的用户 ID
+	hub          *Hub
+	conn         *websocket.Conn
+	send         chan []byte       // 待发送消息缓冲队列
+	UserID       int64             // 关联的用户 ID
+	onDisconnect DisconnectHandler // 断线回调（清理在线状态等）
 }
 
 // NewClient 创建客户端实例
@@ -36,6 +40,11 @@ func NewClient(hub *Hub, conn *websocket.Conn, userID int64) *Client {
 	}
 }
 
+// SetOnDisconnect 设置断线回调
+func (c *Client) SetOnDisconnect(handler DisconnectHandler) {
+	c.onDisconnect = handler
+}
+
 // MessageHandler 消息处理回调函数类型
 type MessageHandler func(client *Client, msg *Message)
 
@@ -45,6 +54,9 @@ func (c *Client) ReadPump(onMessage MessageHandler) {
 	defer func() {
 		c.hub.Unregister(c)
 		c.conn.Close()
+		if c.onDisconnect != nil {
+			c.onDisconnect(c.UserID)
+		}
 	}()
 
 	c.conn.SetReadLimit(maxMessageSize)