diff --git a/core/service.go b/core/service.go
index c5f8210..6ec9943 100644
--- a/core/service.go
+++ b/core/service.go
@@ -360,6 +360,18 @@ func (sh *serviceDescription) link(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	found, err := sh.mongoClient.FindOne(CollectionLink, bson.M{"platform": newType, "uid": newId}, options.FindOne())
+	if err != nil {
+		logger.Error("link failed. FindOne err:", err)
+		w.WriteHeader(http.StatusInternalServerError)
+		return
+	}
+	if found != nil {
+		logger.Println("link failed. already have service account: ", r.URL.Query())
+		w.Write([]byte(`{"alreadylink":true}`))
+		return
+	}
+
 	createtime := primitive.NewDateTimeFromTime(time.Now().UTC())
 	link, err := sh.mongoClient.FindOneAndUpdate(CollectionLink, bson.M{
 		"platform": newType,