Abstract: In analysis of ship global vibration,influence of outboard water should be considered.For studying the global vibration,two methods can be used.One is that 3D finite element model of water domain is applied,and the other is that added mass is introduced into structural matrix for calculation.With the finite element technique developing,3D finite element model of ship is usually taken.However,it is not correct for traditional metho d(such as Lewis added mass method) to neglect the deformation of ship transverse section.We proposed a kind of boundary element method to calculate the 3D added mass matrix of structure with 3D effect,and analyzed the wet structural response.The results show that the method is available and accuracy.