Abstract: The numerical method for fluid-structure interaction analyses based on potential-fluid element was introduced, then the detail of the water - group pile foundation interacted modeling was studied. Taking a deepwater group pile foundation of a bridge as an example, a three-dimensional solid finite element model of the structure and a potential fluid model of water were built in finite element analysis program ADINA, and the dynamic analyses of the model with different depth of water were carried out. In order to investigate the relationship between the hydrodynamic influence and the design geometry of piles and caps, parameter analyses were performed. Main conclusions are: the complete numerical method is an efficient method for dynamic analysis of water - structure interacted system; the convergence of analyses was controlled by the ratio of the gird size of fluid elements on the fluid-structure interface to that of adjacent solid elements; the water-structure interaction has significant influence on dynamic characteristics of the deepwater bridge group foundation; the design of caps and piles causes variation of the fluid-structure interaction, and the hydrodynamic influence can be reduced through reasonable design.