To study the mechanism of cascading failures in a power grid and find out the key vulnerable lines propagating cascading failures, entropy theory and analysis hierarchy process were applied in entropy-weighted fuzzy comprehensive evaluation model, and information of objective data and the subjective opinion of experts were combined in the model to implement effective evaluation and sorting of line vulnerability. The article builds a index system that contains voltage deviation, power flow coefficient and electric betweenness in considering the network structure and real-time running state of the system, and then the lines vulnerability assessment method is proposed .This method can be used to help power grid designers and operators spot the lines prone to black-out. Numerical example results show that the proposed indicators can overcome the deficiency of existing indicators not taking the state of the grid structure and operation into account which proves the assessment method is feasible.
