The key to achieving the economic benefits of shale gas development is to use fracturing technology to form complex fractures and increase the effective range of reservoir transformation. The buried depth of deep shale reservoirs is greater than 3 500 m. In response to the technical challenges of shale fracturing under high stress, a multiphase flow fracturing test system was used to simulate the characteristics of high triaxial stress for hydraulic fracturing tests. The characteristics of fracturing propagation under different stress states were obtained. The research shows that the absolute value of high stress and the vertical stress difference are within 10 MPa, and the main hydraulic fractures can communicate and turn to expand when encountering weak bedding planes. The vertical stress difference is 10 MPa, and the horizontal stress difference is within 10 MPa. The main hydraulic fractures that initiate vertical wellbore fractures can also communicate with natural weak surface fractures perpendicular to the direction of the maximum horizontal principal stress, forming more complex fracture characteristics. The development of natural fractures or weak bedding planes within shale is the material basis for the formation of complex fracturing fractures. If there are no natural weak structural features, the fractures formed after fracturing are all single fracturing fracture surfaces. The fractal dimension of the roughness of the main fracturing fractures under high stress ranges from 2.422 to 2.484, with little difference among different stress states. However, the roughness of natural weak surface fractures is lower than that of the main fracturing fractures. The research results have certain guiding significance for understanding the formation process of shale fractures under high stress state.