Abstract: To improve the operation security level of power grid, an identification method of vulnerable lines for fault propagation in power grid based on the weighted power flow entropy is put forward. The DC power flow method is used to estimate the power increment and load rate of other transmission lines when line disconnection fault occurs. The weighted power shock entropy is used to reflect the effect of the power flow transferred from other disconnected transmission lines on the goal transmission line, and the weighted flow distribution entropy is applied to reflect the influence of the disconnection of the goal transmission line on the distribution of load rate in power system. By combining the weighted power shock entropy and the weighted flow distribution entropy, the comprehensive vulnerability index is defined to identify the vulnerable lines for fault propagation in power grid. The direct current power flow method can accurately estimate the line power when line disconnection fault occurs through simple mathematical calculating, which has such advantages as less computation amount and good applicability. Both the impacted vulnerability and the disconnected consequence vulnerability of transmission lines are used to reflect the vulnerability of transmission lines for fault propagation. At the same time, the weighted power flow entropy can reflect the risk of the high load rate even overload. In the end, the method is verified in IEEE 39\|bus system.