Abstract: The particle materials are characterized by discontinuity and dispersion, so they face great computational pressure in numerical simulation. The exact scaling criterion and coarse-grained method are introduced into the combined finite-discrete element method (FDEM) to provide a solution for accelerating the numerical simulation of granular materials based on the FDEM. Based on the theories of exact scaling and coarse granulation, the exact scaling criteria for the FDEM are derived. On this basis, the numerical triaxial shear tests for equal diameter particle system and binary particle system are carried out respectively. The test results show that without the introduction of the exact scaling criteria, the mechanical response characteristics of the coarse-grained model will change, resulting in distortion, and the parameters of the coarse-grained model need to be corrected. After the introduction of the exact scaling criteria, the mechanical response characteristics of the coarse-grained model are corrected. The test results demonstrate the effectiveness of introducing the exact scaling criteria and coarse granulation method into the FDEM. It can greatly improve the computational efficiency of numerical simulation of granular materials using the FDEM under the similar conditions to the original particle system. Based on the numerical test results, the macroscopic stress deformation and mesoscopic contact force are correlated, and the micromechanical mechanism of the exact scaling and coarse-grained methods is revealed.