Abstract: Stability of seabed in response to ocean wave loading is an important consideration in the design of offshore structures. To describe the strain characteristic of cohesionless soils under cyclic loading, a framework of a practical constitutive model is proposed and model parameters of a silt are obtained mainly from un-drained dynamic triaxial tests. Plastic strain of soils under cyclic loading can be calculated from initial stresses state, cyclic stresses and its duration in the process of FEM calculation, and the elasto-plastic matrix relating stress and strain is not needed. Biot's consolidation equation is applied in the FEM Program developed by the authors. Variation of effective stresses of silt seabed response to progressive waves is given. Numerical results agree well with the wave tank test results in trend.