diff --git a/nebula3/gclient/net/SessionPool.py b/nebula3/gclient/net/SessionPool.py
index c3ad435c..658b2599 100644
--- a/nebula3/gclient/net/SessionPool.py
+++ b/nebula3/gclient/net/SessionPool.py
@@ -456,8 +456,9 @@ def _remove_idle_unusable_session(self):
 
                 # release idle session and remove from the pool
                 if idle_time > self._configs.idle_time:
+                    conn = session._connection
                     session.release()
-                    session._connection.close()
+                    conn.close()
                     self._idle_sessions.remove(session)
 
     def _period_detect(self):