Abstract: Hydraulic fracturing simulation experiments of shale outcrops were carried out by a true triaxial test system. The effects of multiple factors on fractures propagating law of horizontal well in shale formation were studied, and fracture morphology were observed by high-energy CT scanning. The results show that there is a certain range for the effects of delivery rate on fracture complexity. When the horizontal stress difference is less than 9 MPa, hydraulic fracture easily propagates along the natural fractures, forming fracture network. In this range, when the stress difference is increased, the main hydraulic fracture (transverse fracture) can be formed more easily and communicate more natural fractures, forming a relatively more complex fracture system. Under the condition of the same horizontal stress difference, if the stress difference coefficient is greater than 0.25, the obvious single main fracture will form. The effects of viscosity of fracturing fluid and delivery rate on fracture propagation can be expressed by the parameter qμ. Too small or too large value show that fracture network is not easy to produce. The development and cementation intensity of shale depositional bedding seriously affect the fracture propagating complexity of hydraulic fracturing.