In order to study the casing deformation and its causes in the process of multi-stage fracturing of shale wells, a full-scale multi-stage fracturing finite element model of formation and casing is established based on the actual wellsite data. The overall deformation of the horizontal section casing and the deformation of the casing at the natural fracture after each stage of fracturing are clarified. The hydraulic fracture expansion and in-situ stress disturbance after each stage of fracturing are explained. The influencing factors of shale gas casing deformation are studied by changing hydraulic fracturing treatment parameters. The results show that the multi-stage fracturing of shale gas wells will cause the formation creep and the change of the in-situ stress field near the fracturing zone, which will damage the casing. As the fracturing continues, the casing deformation will gradually increase. With the increase of construction displacement, the angle between fracture and casing decreases, and the spacing between fracturing sections decreases, which will all increase the probability of natural fracture slip and cause more serious casing deformation. The research can provide reference for preventing and controlling casing deformation caused by fault slip.