Hydraulic fracturing stimulation is widely conducted to enhance hydrocarbon production in low-permeability reservoirs. However, the massive fracturing can lead to the well failure by compromising well integrity. In this thesis, the mechanism of casing deformation in shale reservoirs during hydraulic fracturing process is studied. The statistical analyses show that shear slip of weak rock is closely related to casing failure. To investigate the shear slip of rock and its effect on casing deformation, a two-dimensional finite element model (FEM) of injection-induced deformation under hydraulic fracturing is established. The poro-elastic constitutive relation is used to analyze the changes of stress and flow during hydraulic fracturing. In the model, fracture growth is simulated with cohesive zone model (CZM), and the result of slip displacement can be used to predict casing deformation. Lastly, parametric analysis is conducted to show the relationship between different parameters and the formation deformation as well as natural fracture slippage. The fracture slip causes large casing shearing deformation. This study concludes that the shear deformation induced by the slippage of shear fractures during hydraulic fracturing have a big influence on casing integrity and can be inferred as a major casing failure mechanism. In the casing deformation mechanism study, this work quantitatively predicts the rock slippage during fracturing under various conditions using finite element models. The findings can be used to forecast formation/wellbore response and casing deformation under hydraulic fracturing, which supplies technique support for safe and effective shale gas development.