Many hydroelectric power stations are constructed on rock foundations. Therefore, the stability of rock slope is critical for the engineering especially in the excavation state. The analysis for consequent rock slopes is not identical with the earth slope because of their material characteristics. In this paper, it is combined the elastic-plastic finite element method and safe factor strength reduction method for the solution of problem. Considering the multi-layer material of the rock slope, Drucker- Prager criterion is adopted for determining the yield station which has the modified format of Morh-Coulomb criterion overcome the corner point problem of application proper for rock material. The conditions both of displacement mutability and cut-through of plastic zone are described in detail and research deep for failure judged. Analysis and compare of the situations which contain displacement, plastic zone between pre-excavation and post-excavation by certain numerical example, some useful results are given for stability analysis of consequent rock slope.