Abstract: Nonlinear seismic analysis of concrete gravity dam is performed based on the plastic damage theory. The hysteretic characters, energy dissipation ability, failure mechanism and characteristics are researched. A seismic damage assessment model which can consider damage energy dissipation is developed for describing the damage degree of dams during strong earthquakes. The results show that the dam head are the vulnerable parts of gravity dam. The vibration energy and the earthquake responses of structure are reduced effectively by the structural damping, little amount seismic energy is dissipated by concrete damage and plastic dissipation. The seismic damage assessment model can quantitatively evaluate the damage degree of gravity dams during strong earthquake.