To clarify the evolution law of in-situ stress and its impact on fracture stability during the fracturing process of shale gas reservoirs in a block of southern Sichuan, a three-dimensional geological model was established to investigate the evolution law of in-situ stress during single-well and multi-well fracturing, and the coulomb failure function (CFF) was used to evaluate fracture stability. The results show that during single-well fracturing, the change of in-situ stress is mainly concentrated near the wellbore and fractures: the disturbance of the maximum horizontal principal stress ranges from -3~6.5 MPa, the disturbance of the minimum horizontal principal stress ranges from -4~ 10 MPa, the disturbance of the CFF value ranges from -3 ~4.5 MPa, and a total of 7 fractures become unstable. During multi-well fracturing, the existence of stress superposition and stress shadow effect between inter-well fractures leads to a wider range and greater intensity of stress change: the disturbance amplitude of the maximum horizontal principal stress reaches -5~13 MPa, the disturbance amplitude of the minimum horizontal principal stress reaches -10~14 MPa, the disturbance of the CFF value ranges from -3.8~6 MPa, and a total of 31 fractures become unstable, including 21 between wells. It can be concluded that inter-well interaction in multi-well fracturing is a key factor leading to the increased risk of fracture instability. Therefore, when optimizing the fracturing scheme, emphasis should be placed on the stress changes in the inter-well area and fracture stability to improve shale gas recovery and ensure the safety of the mining process.