Abstract: The concept of active power transferring coefficient is put forward,with the active power transferring coefficient of multi-line resection derived via the calculating method of DC power flow.When excision of many lines happens,by using the breadth priority search algorithm in graph theory,all the lines are searched level by level.Meanwhile,their active power transferring coefficients are calculated to quickly search out the transmission section greatly influenced by power flow transferring,while solving the problem of leaving out the line whose power flow increases reversely.Neither large-scale matrix operation nor search of whole network topology is needed.Finally,an IEEE 30 node system simulation is analyzed that shows the feasibility and effectiveness of the algorithm.