Abstract: By reconstructing the meso-structure of granite using the particle flow software PFC^2D based on the grain-based model, a series of conventional triaxial compression tests on granite under different confining pressures are carried out. The relationship between the heterogeneity of the meso-structure caused by crystal size distribution and the parameters of Mohr-Coulomb strength criterion and Hoek-Brown strength criterion as well as the brittleness of rock is revealed. The heterogeneity has a significant effect on the stress-strain curve of rock specimens under pressure loading. As the heterogeneity factor increases, the rock changes from homogeneous to heterogeneous, the elastic modulus decreases, and the Poisson's ratio increases. As the heterogeneity factor increases, the compressive strength of the rock decreases, the cohesive force increases, and the internal friction angle decreases. For the same type of granite, the values of the Mohr-Coulomb strength criterion and the Hoek-Brown strength criterion are not constant, but depend to some extent on the internal meso-structure. When the meso-structure of the rock changes, the parameters in the two strength criteria also change. The heterogeneity of the meso-structure has a great influence on the brittleness index of rock. With the increase of heterogeneity factor, the brittleness index decreases.