In view of the cascading trip induced by backup relays that affects the safe operation of the system and may even cause blackout,after investigating the defects of the existing backup protection,this paper presents a robust fault-tolerance control by backup relay protection scheme based on identifying the flow transfer,and proposes to estimate the dynamic flow distribution after flow transfer occurs.The simulation in a New-England 10-machine 39-node network by the sofesare of PSASP shows that the backup protection strategy proposed to identify flow transfer works well.