Abstract: More accurate and rapid identification of the key lines of power grid is of great significance to improve the stability of the power grid operation and prevent cascading failure of power grid. Firstly， on the basis of the complex network theory， the improved flow betweenness index is proposed to judge the vulnerability of the branch from the structural point of view after the power disturbance. Then， on the basis of the entropy theory， the weighted flow transfer entropy index considering the load rate of the branch is proposed， which overcomes the shortcomings of the original indicator only considering the uniformity of the transfer flow distribution. Finally， the comprehensive importance assessment index including above two indicators is established to more comprehensively measure the importance of the branch in the power system. Through the simulation， the improved network transmission efficiency curve of the system under different attack modes is obtained. The effectiveness of the method is proved by the simulation of IEEE 39-node system， which is of great significance to prevent the cascading failure of power system.

Key words: the cascading failure, improved flow betweenness, weighted flow transfer entropy, comprehensive importance index