Abstract: The principal stress axis rotation was occurred widely for dams under wave loading. Based on the elasto-plastic constitutive model of sands considering the effects of a cyclic rotation of principal stress axes, the pragmatic stress integration algorithm of the model was developed and incorporated into the FEM software of MSC. Marc, used to analyze the deformation of a typical dam under wave loading. Results show that the deformation tendency of the dam in the horizontal direction is along the side of wave loading application and that in the vertical is the settlement to the bottom. Meanwhile it is found that the deformation of the dam is influenced greatly if the effects of principal stress axis rotation are considered. Compared with the deformation of the dam with and without effects of principal stress axis rotation, the effects of principal stress axis rotation will occur in the following aspects: 1) increasing the maximal horizontal and vertical deformation; 2) enlarging the deformation area; 3) affecting the distribution of the deformation. The dangerous design may be induced if the effects of principal stress axis rotation are not considered in the real projects.