A vulnerability assessment model for cascading failures of complex power grid based on effect risk entropy and the implementation of algorithms are discussed.First，a branch vulnerability assessment model is proposed by referring to the power flow transfer and its distribution characteristics after branch outage，and the impact of disconnected branch on the power system is also taken into account in the model.Then，the vulnerability transitive relation between nodes is considered，and the method is able to overcome the existing inadequacy of currently used social network index and system science index.Finally，the risk uncertainty faced by the grids structure is identified based on vulnerable components assessment results.The test on an IEEE39-bus system demonstrates the rationality and validity of the method proposed in comparison with other methods available.