Abstract: Under cyclic loadings,the plastic strain of soft soil would be happened under very small shear strain.So the visco-plastic model was appropriate to be used to simu late the dynamic characteristics of soft soils.Based on the principles of geotechnical plastic mechanics,the incremental visco-plastic memorial nested yield surface model was developed using the nonlinear isotropic and kinematic hardening modulus field theory.At the end of any increment,the inverted loading surface,the failure surface and the initial loading surface witch was tangent with the inside of inverted loading surface were memorized,and dynamic behavior of yield surface was defined by these surfaces.The developed model was implemented in ABAQUS software successfully.The predicted stress-strain relationship of soil were compared with the test results given by cyclic triaxial tests.It was proved that the cyclic undrained stress-strain relation of soils could be fairly simulated by the model.At last,the nonlinear earthquake response of a representative soft site in Nanjing was calculated with the dynamic behavior of soils modeled by the developed model.The results coincided with the earthquake response of soft site given by others.