In order to estimate the stability of the surrounding rock for cavern group of underground powerhouse at right bank of Suofengying Hydropower Station, the numerical simulation of the initial stress field , the excavating scheme, the excavating process, reinforced measures, stress and deformation of the surrounding for the underground cavern group are carried out by adopting a self-developed 3D Elastoplastic FEM program. The results of numerical simulation indicate that the stability of the underground cavern group is good enough to meet the requirement of engineering design and provide the guidance for engineering design and construction.