Abstract: A good understanding of rock cutting mechanism is of great importance for improving the cutting efficiency and reducing the costs in hard heterogeneous formation drilling. Implements the grain-based modeling approach to mimic the granite considering the highly heterogeneous mechanical behaviors of grains in granite. The rock cutting mechanism of granite, accounting for the influence of hydrostatic pressure, mineral size, random distribution, rake angle, cutting depth and velocity of cutter, are investigated. The research results demonstrate that the inter-grain shear crack and intra-grain tensile crack are the two main crack types generated during rock cutting process. The cutting force responses show strong vibration with respect to the cutting distance. The magnitude of cutting force sharply drops and abruptly rises during the cutting process, which becomes more obviously with the increasing hydrostatic pressure, cutting depth and rake angle of cutter. The hydrostatic pressure, grain size and random distribution of grains have great influence on chip morphology. In contrast, comparing with the above three factors, the cutting depth, rake angle of cutter and cutting velocity have little influence on the chip morphology. These results lead to an enhanced understanding of rock breaking mechanisms in granite, and provide a basis for improving the design of rock-breaking bits.