Abstract: Considering the nonlinear characteristics of dilatancy and strength of coarse-grained materials, an elastoplastic constitutive model based on microstructures is established within the framework of classic elastoplastic theory. In the model, a yield function derived from the microstructure of granular materials is adopted,and a stress-dilatancy relationship is developed from the yield function with the non-associated flow rule. Based on the typical trixial compression test results of coarse-grained materials, a hardening parameter is proposed by introducing a compression model for cohesionless soils, which can describe both the dilantancy and the contraction of coarse-grained materials. The proposed model has 7 parameters, which can be determined by the conventional trixial compression tests and the isotropic compression tests. The proposed model is calibrated by modeling the trixial compression tests on three rockfill materials. It is found that the calculated values are in good agreement with the experimental data, indicating that the proposed model can reflect the stress and deformation characteristics of coarse-grained materials reasonably.