diff --git a/src/common/db/model.go b/src/common/db/model.go
index f34b4c305..f8be3747a 100644
--- a/src/common/db/model.go
+++ b/src/common/db/model.go
@@ -22,7 +22,6 @@ func key(dbAddress, dbName string) string {
 func init() {
 	//mysql init
 	initMysqlDB()
-	// mongo init
 	mgoDailInfo := &mgo.DialInfo{
 		Addrs:     config.Config.Mongo.DBAddress,
 		Direct:    config.Config.Mongo.DBDirect,
@@ -40,6 +39,11 @@ func init() {
 	DB.mgoSession = mgoSession
 	DB.mgoSession.SetMode(mgo.Monotonic, true)
 
+	c := DB.mgoSession.DB(config.Config.Mongo.DBDatabase).C(cChat)
+	err = c.EnsureIndexKey("uid")
+	if err != nil {
+		panic(err)
+	}
 	// redis pool init
 	DB.redisPool = &redis.Pool{
 		MaxIdle:     config.Config.Redis.DBMaxIdle,
diff --git a/src/common/db/mongoModel.go b/src/common/db/mongoModel.go
index 6d315193e..a0fbbfb18 100644
--- a/src/common/db/mongoModel.go
+++ b/src/common/db/mongoModel.go
@@ -22,6 +22,7 @@ type MsgInfo struct {
 type UserChat struct {
 	UID string
 	Msg []MsgInfo
+	BId bson.ObjectId `bson:"bid"`
 }
 
 type GroupMember struct {
@@ -155,12 +156,15 @@ func (d *DataBases) SaveUserChat(uid string, sendTime int64, m proto.Message) er
 
 	log.NewInfo("", "get mgoSession cost time", getCurrentTimestampByMill()-newTime)
 	c := session.DB(config.Config.Mongo.DBDatabase).C(cChat)
-
+	err := c.EnsureIndexKey("uid")
+	if err != nil {
+		log.NewError("", "EnsureIndexKey uid failed ", err.Error())
+	}
 	n, err := c.Find(bson.M{"uid": uid}).Count()
 	if err != nil {
 		return err
 	}
-	log.NewInfo("", "find mgo uid cost time", getCurrentTimestampByMill()-newTime)
+	log.NewInfo("", "find and create index mgo uid cost time", getCurrentTimestampByMill()-newTime)
 	sMsg := MsgInfo{}
 	sMsg.SendTime = sendTime
 	if sMsg.Msg, err = proto.Marshal(m); err != nil {