Abstract: 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 FDEM. Based on the theories of exact scaling and coarse-granulation, the exact scaling criteria for FDEM are derived. On this basis, the numerical tests of triaxial shear for equal diameter particle system and binary particle system are carried out respectively. The test results demonstrate the effectiveness of introducing exact scaling criteria and coarse-granulation method into FDEM. It can greatly improve the computational efficiency of numerical simulation of granular materials using FDEM under the condition of similar 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.