Critical segments in power system are closely related to cascading failure and provide important bases for dynamic monitoring and emergency control. In order to identify the critical segments, a novel method of vulnerability evaluation of power grid and cascading failure searching based on uncertain multiple attribute decision-making is proposed. Firstly, according to the relation between the branch and the protection relay on the branch, the initial fault event set is established and the decision matrix is formed in the real time by taking the various factors that trigger a chain of failures into account. By adopting the multi-attribute decision making based on information entropy, the initial fault events are sorted. By comparison with the threshold set, the proper initial fault event is screened; then the subsequent fault is searched based on the improved branch operational reliability model; finally, the fault sequence, node and the entire system are assessed by vulnerability function. The simulation results show the method has a good application prospect.