Abstract: Based on the observation of the core of a well in the shale gas field in southern Sichuan at the mesoscale and the construction of a two-dimensional fracture model, displacement discontinuity method was used to simulate the physical and mechanical process of the interaction between hydraulic fractures and natural fractures in deep shale hydraulic fracturing. The influence of principal stress, stress difference and fracturing fluid injection rate on fracture propagation were discussed. The results show that under high stress difference, the length of the fracture decreases, the average width of the fracture increases and the increasing of fracture average width due to the increase of injection rate becomes limited. New fractures prevail in the increase of fracture length with the injection rate increases, so as to improve the activation of natural fractures, but the effect is limited. The generation of shear fracture is more affected by principal stress and injection rate, and its length decreases significantly under high stress difference. The fracture length under low injection rate is gradually larger than that under high injection rate during the fracturing process, under the condition of lower stress difference and the same injection volume. Fracture propagation rate decreases under high stress difference and generating more new fractures due to increasing the injection rate becomes limited. The modeling results based on the microscope observation meet the actual site better, and provide a reference for the design and construction of deep hydraulic fracturing in shale gas reservoir.