Dynamic finite element analysis for a RCC gravity dam is implemented by using response spectrum method in this paper. Firstly, three-dimensional finite element model is established, and then the subspace iterative method is used in the modal analysis of the gravity dam. The natural vibration frequencies, the natural vibration period and modes are obtained. The response spectrum method is employed to implement dynamic analysis of the gravity dam. At last, the combinations of both the static and dynamic stress are made with the principle for extreme strength condition, seismic dynamic response of the dam is investigated.