Based on the concept of state parameter

the peak stress ratio and dilatancy ratio are regarded as the function of state parameter; and meanwhile the initial modulus changing with confining pressure is considered; then an elastoplastic model for coarse grained soils and its parameter calibration are proposed. The model expression is simple and its concept is clear; it can describe the strain softening and dilatancy over a full range of densities and stress levels and its dependency on physical state and effective confining pressure. The validity of the model is confirmed in predicting triaxial compression test results of coarse grained soils.