Considering two-way fluid-structure interaction and using finite element software ANSYS simulation study of cylindrical pier at different flow rates caused by the interaction of the river and pier piers vibration problems, through the discrete solution of wet modal method, and combined with engineering example, the analysis results using Lanczos method extraction, introduction of green's function of point source, using the finite element-boundary element analysis wet modal and wet frequency of the structure. Numerical results show that: Frequencies of wet modal than no fluid medium under the influence of modal frequencies is much lower. So for underwater structures, when analysis the modal,it is must be considered the fluid influence of wet modal.