Inevitably, high pressure groundwater, upland stress and the problems controlled and induced by the two factors will come out during deep-buried tunnel excavation, so the analysis of influence of water pressure on surrounding rock stability will be of high significance. In order to study the influence, FLAC3D is used for the numerical simulation analysis of Jinping Ⅱ Hydropower Station. Through calculation of the maximum deformation of the surrounding rock under different conditions of water stress, the relationship between the deformation of surrounding rock and the water pressure is established and the critical water pressure is solved. When the rock strength meets some conditions, the water pressure influence on the stability of surrounding rock can be ignored if the water pressure is less than the critical water pressure. The results of numerical simulation analysis show that the surrounding rock of marble Ⅱ can be ignored and high water pressure has a great influence on the surrounding rock of marble Ⅲ which suffers a severe deformation and it is necessary to support.