Aiming at the problem that existing micro-computer based five-prevention devices cannot distinguish the state of grounding knife switch（GKS） at the other end of transmission line， which may result in mal-operation of closing GKS， a transmission line closing inter-station locking system which reflects the state of GKS is proposed. Through acquisition of GKS state information at the other end， locking or unlocking commands are issued to breaker close-switching control circuit of primary end， the locking of breaker grounding isolator can maintain so as to prevent occurrence of mal-operation fault and improve the operation reliability of power system.