Based on the laboratory tests on granite， a two-dimensional discrete element simulation method（DEM） of granite based on digital image was studied. Based on the pictures of granite photos，the micro-structure model of granite was reconstructed by digital image technique and the DEM numerical model was established through the reconstructed model. A uniaxial compression test was conducted by the particle flow program （PFC） to calibrate the parameters used in the model. With the use of these obtained parameters， the mechanical properties of granite were studied by two-dimensional numerical biaxial tests，and the deformation and failure mechanism were discussed from a microscopic perspective.The whole process of loading and the morphology of micro-damage were studied in the numerical experiment，and the results were compared with the indoor test results. The results show that the strength characteristics of granite obtained from digital image granite biaxial compression test， the development process of micro-cracks and the specimen failure characteristics are in good agreement with those from laboratory tests. The two-dimensional particle-based discrete element method based on digital image can describe the characteristics of micro-damage of granite with obvious discontinuities in uniaxial and biaxial compression state，and provides an effective method for the further investigation on complex stress conditions under the destruction mechanism.