Abstract: Casing failure is a common geological disaster in the process of oil and gas exploration. Most previous studies in this field mainly focused on vertical casing damage of conventional oil and gas. However, because of the angle's difference between two casings and steep fault and the creep strength's distinction between two reservoir media, the horizontal casing failures in shale gas have different mechanism from the vertical in conventional oil and gas. For this reason, this paper studied the damage of horizontal casing which through fault in shale gas. Through mechanical analysis and numerical simulation of casing deformation, it was found that creep force of the surrounding rocks could cause necking before fault slip. And it performed differential deformation near the fault because of the lithological difference between hanging wall and footwall. With the activation of fault caused by hydrofracking and reservoir exploitation, the shear force from fault deformation played a major role in casing bending or dislocation problems. The result of numerical simulation is consistent well with the mechanical analysis which indicates that horizontal casing failure is the combined action of compressional force from rock creep and shear force from fault slip.