Abstract: It is important to use the existing structure of the power grid to reduce the blackout of the users. Loop closing operation can reduce power outage, but it is dangerous. Real time security calculation is very necessary. Through the improved multi-balance buses power flow calculation and weighted robust state estimation, DSA technology is applied to real-time loop closing security check for distribution network. Applying the theory, the Tianjin electric power dispatching control center and Chengxi electric power dispatching control center have realized the synchronous online safety analysis under the DSA. And the power outage reducing and security is achieved.