Abstract: To deeply understand the hydraulic fracturing crack propagation rule of shale gas reservoir and crack network formation conditions， a two-dimensional model of hydraulic fracture extension in shale was established. The influence of in-situ stress difference coefficient， natural fracture and bedding plane on hydraulic fracture extension was analyzed， and the mechanism of hydraulic fracture network formation was studied. The results show that the steering and bifurcation of hydraulic fracture along the bedding plane and coalescence into natural fracture are the keys to the formation of crack network. Crack network can form on condition that the approaching angle between bedding plane and natural fractures and the stress difference coefficient are combined properly with critical values， or a single crack will form. The fracture network in shale gas reservoir is easy to form when the angle is large between the maximum horizontal principal stress direction and bedding plane or natural open fracture.

Key words: shale gas, hydraulic fracturing, crack network, stress difference coefficient