Abstract: On the basis of rock mass quality evaluation and model summarized,finite element numerical modeling technique is used to systematically analyze the distribution of stress filed,strain field and plastic zone in the surrounding rock mass of the underground cavities after excavation in the Dagangshan hydropower station. After the underground cavities excavation,stress concentration of varying degrees appear around the corner of cavities,and some plastic zones exist around the cavities,which are mainly extensional damage.It is proposed taking appropriate support measures when excavating.The main results can be taken as the basic data and the theoretical proofs to evaluate cavities stability and guide correct excavation.