Geogrid has a certain influence on the strength and deformation characteristics of coarse-grained materials. In order to investigate the constitutive model which can reasonably describe its strength and deformation characteristics, based on the conventional triaxial test results of geogrid reinforced coarse-grained materials, a nonlinear dilatancy equation is proposed in this study to reasonably describe the dilatancy and shrinkage characteristics of geogrid reinforced coarse-grained materials according to the characteristics of dilatancy of different types of geogrid reinforced coarse-grained materials. On the basis of above studies, combined with the theory of generalized plastic model, an elastoplastic constitutive model that can reflect the deformation and strength characteristics of geogrid reinforced coarse-grained materials is proposed. There are totally 6 parameters in the model, all of which can be determined by conventional triaxial test. Finally, the accuracy of the model is fully proved by simulating the static and dynamic triaxial tests on geogrid reinforced coarse-grained materials under different confining pressures.