Abstract: Hydraulic fracturing breaks tight shale by injecting a large amount of fracturing fluid under high pressure. The potential impact of this process on the surrounding environment, such as hydraulic fracturing-induced reactivation of faults, has received extensive attention from society. In order to develop shale gas more safely and reasonably, optimize hydraulic fracturing construction design, and reduce its impact on the surrounding environment, it is necessary to carry out research on the evolution of reservoir in-situ stress and fault stability during the water injection process of hydraulic fracturing. In this work, the properties of pore pressure diffusion, volume strain variation in fault fracturing zone, and fault stability were analyzed based on the fluid-solid coupling method, focusing on the enhancement of reservoir conductivity after the hydraulic fracture network connects with the natural fractures. The injection pressure refers to the hydraulic fracturing pressure in Southwestern shale gas reservoirs in China. Results show that with the progress of the water injection process, the pore pressure diffusive zone increases, and the effective stress near the fault zone decreases, which induces a higher risk of faults reactivation. The volumetric strain of the fracturing zones on both sides of the fault presents an opposite trend, either in compression or extension. The pore pressure field in the fault fracturing zone and fault core adjacent to the injection well increases significantly(the increment ratio is around 1.1), resulting in the local instability of the adjacent fault, but the entire fault zone is stable.