The discrete element method is a numerical method used in non-continuum. It is suitable for high rock slope contained much more rock faults,joints and cracks to do analysis of stability. The strength reduction method is a numerical method, which is applied in slope analysis of stability extensively. Strength reserve coefficient assessed by strength reduction method is equal to stability safety factor proposed by limit equilibrium method. The discrete element method and strength reduction criterion are combined. Two kinds of grid are used, i.e. dense grids represent the condition of joints and cracks development,and the thin grids are approximately equal to condition which rock integrity has been improved because of reinforcement.The simulation of water cushion pool high rock slope of Goupitan Project is done, the stability of natural slope and excavation slope analyzed, and supporting effect evaluated.