Based on the Morison equation method， the influence of the dynamic water pressure was considered by using the additional mass. The rigid foundation bridge pier and the bridge pier structure taking into account SSI effect under the dynamic water pressure were established by using ABAQUS software computing platform. Then the seismic responses of the bridge pier structure with and without consideration of SSI effect were com- pared under the dynamic water pressure. Finally， the change regulation of seismic response of bridge pier at dif- ferent water depths considering SSI effect was analyzed. The research results show that under the dynamic water pressure， the seismic response of the pier increases， and it is influenced by underwater penetration of bridge pier; when considering SSI effect， the dynamic water pressure on the decrease of the natural vibration frequency and the increase of the seismic responses are reduced. However， the dynamic water pressure can not be neglect- ed.