Abstract: The monitoring of hydraulic fracture shows that the morphology of hydraulic fracture in shale reservoirs is complex, and is essentially different from that in the traditional sandstone reservoirs. The traditional models for fracture propagation are difficult to describe and explain the complexity of fracture propagation in shale formation. Based on the theory of linear elastic fracture mechanics, in accordance with fracture development characteristics in shale formation, a 2D numerical model for multi-fracture propagation is established by adopting the displacement discontinuity method. This model simulates the complex morphology of hydraulic fracture propagation under the interference of randomly distributed natural fractures in shale formation. Numerical simulations show that when the relative net pressure is high, the angle between natural fracture and optimized propagation direction of the initial hydraulic fracture is large, and it is more liable to create complicated fractures. And when horizontal stress difference is larger, it is less liable for hydraulic fractures to branch. The true tri-axial hydraulic fracturing tests on shale outcrops further validate the reasonability of this numerical simulation method. The results of micro seismic monitoring interpretation of Longmaxi shale formation agree well with the numerical results in this paper.