diff --git a/src/client/src/tscSql.c b/src/client/src/tscSql.c
index ef8625da06c349b14b9bc9294462bf627da5bb5b..f73b4abb159852a4db1e8ff52e07d0965b83c821 100644
--- a/src/client/src/tscSql.c
+++ b/src/client/src/tscSql.c
@@ -257,10 +257,21 @@ TAOS *taos_connect_a(char *ip, char *user, char *pass, char *db, uint16_t port,
 void taos_close(TAOS *taos) {
   STscObj *pObj = (STscObj *)taos;
 
-  if (pObj == NULL || pObj->signature != pObj)  {
+  if (pObj == NULL) {
+    tscDebug("(null) try to free tscObj and close dnodeConn");
     return;
   }
 
+  tscDebug("%p try to free tscObj and close dnodeConn:%p", pObj, pObj->pDnodeConn);
+  if (pObj->signature != pObj) {
+    tscDebug("%p already closed or invalid tscObj", pObj);
+    return;
+  }
+
+  // make sure that the close connection can only be executed once.
+  pObj->signature = NULL;
+  taosTmrStopA(&(pObj->pTimer));
+
   SSqlObj* pHb = pObj->pHb;
   if (pHb != NULL && atomic_val_compare_exchange_ptr(&pObj->pHb, pHb, 0) == pHb) {
     if (pHb->pRpcCtx != NULL) {  // wait for rsp from dnode