In view of the possible serious consequence of hydropower structure under seismic action,the influence of dynamic water pressure produced by seismic on the vibration characteristics of hydropower structure has become an important control factor of hydropower structure design. Combining with practical powerhouse engineering of a riverbed-hydropower station,the paper used ANSYS as a platform to establish three-dimensional finite element model and analyze the influence of seismic dynamic water pressure on the vibration characteristics of hydropower structure. The results shows that seismic dynamic water pressure increases the added mass of dam surface,and then reduces the vibration frequency of powerhouse itself,and has certain influence on vibration mode, especially the local vibration mode changes of water inlet gate pier and draft tube gate pier etc. So it is necessary to analyze the frequency of natural vibration under the effect of seismic dynamic water pressure; with the reduction of upstream water level,the overall quality of hydropower is decreased and the frequency of natural vibration of hydropower under the action of seismic dynamic water pressure is increasing.The vibration modes of powerhouse under different water levels are obviously changed.