With the development of smart grid,the interconnection level of power systems is being enhanced so that it is very important to strengthen the security and stability analysis to prevent blackouts.Power system vulnerability identification is the prerequisite and foundation of power system security and stability assessment.Based on the complex network theory,we establish a comprehensive vulnerability index combining with the actual power grid operation,improve the line-efficiency definition using active value of transmission power flow,and identify vulnerable buses and transmission lines through calculating global efficiency variation when network topology or operation status changes.Simulations show that the transmission lines which are closely related to the power sources and key hub buses have great impacts on the overall vulnerability index of power systems.