Abstract: A comparative study was performed on the calculation methods of earthquake hydrodynamic pressure between Chinese and Japanese seismic codes of bridges through a calculation example of a deepwater pier,and the similarities and differences of both the methods were analyzed.A huge difference was obtained from both the results.The earthquake hydrodynamic pressure of a pier in deep water was calculated by numerical simulation and the distribution of pressure along the pier height was investigated.A finite element model of the 260-meter-span Ushine Bridge was built and an added mass method was applied to the model to study the influence of earthquake hydrodynamic pressure on the performance of the whole bridge. The results showed that the displacement and moment obtained by the added mass method was rather more than those without consideration of water. In the performance-based design theory of deepwater bridges and its application field, more studies were needed on the problem of the interaction between piers and water.