Power system’s weak point analysis commonly uses sensitivity analysis method. This paper presents a new identification method of weak points based on loop bulk power system reliability of adequacy evaluation. The method puts the loop reliability parameters as input parameters to assess the reliability of the bulk power system, and determines the important degree of circuit elements based on Birnbaum constant method. To better distinguish the weak point in the system, this paper deduces loop contribution indices on the basis of the traditional grid system reliability evaluation indices. The system-loops-node three levels reflect the reliability of the electrical network and weak points. The actual assessment of province's power grid indicates that the method can effectively reduce the number of system status without complex sensitivity calculation, and overcome the problem that the traditional system reliability index can’t accurately find the weak points.