With the underground powerhouse in Rongge power station as a case study, three-dimensional non-linear finite element method was employed to simulate the dynamic process of excavation and supporting of cavern groups. The anchor was simulated by implicit bar element and the concrete spray layer was simulated by shell element. The regularity of stress deformation distribution of the surrounding rock during dynamic excavation, development of plastic zone in the surrounding rock, and the variation of anchor stress were obtained. Results showed that the variation of surrounding rock displacement was normal and the value was very small. The plastic zone  mainly distributed around the underground caverns and the surrounding rock was stable during the whole excavation. However, the surrounding rock displacement was larger in the intersection of caverns, and wide plastic zone appeared there. Optimized supporting measure was put forward, and the effect was assessed.