In order to prevent the cascading line overload trip， an adaptive strategy for adjusting backup protection operation characteristics is studied. The concept of power transferring area is defined to describe the influence scope of power transferring caused by branch removal events， and the method for searching power transferring areas is provided based on graph theory. To avoid immediate overload trip of backup protection caused by initial branch removal events， the rapid searching method for adaptive strategy is proposed. Finally， the implementation logic of adaptive strategy is also given to avoid undesired overload trip of backup protection on basis of reliable clearance of internal short-circuit fault. Simulation results demonstrate the effectiveness and necessity of the proposed method.