On the basis of the potential fluid theory, the effect of hydrodynamic force on the dynamic response of a typical rectangular solid pier as prototype was analyzed at different water depths under two types of seismic waves. At the same time, the distribution of the hydrodynamic pressure, the action spot of the hydrodynamic force and the effect of fluid on the seismic response of the piers were analyzed in seismic waves. The results include the vibration period, the peak of displacement, shear and moment of pier are increased as the rise of water depth. The effect of fluid on the dynamic response of pier should not be ignored. The influence of different seismic loads on the distribution of hydrodynamic pressure is not identity.