In this paper, a double-layer casing structure is proposed to alleviate the casing deformation during the multi-stage fracturing of horizontal Wells in shale gas. A numerical calculation model of double-layer casing structure with fault slip shear is established, and the shear load and deformation of conventional single-layer casing and double-layer casing under fault slip condition are compared. The factors influencing the shear load and deformation of double casing structure are analyzed. The results show that the double-layer casing structure can significantly reduce the casing deformation through the axial sliding and annular clearance of the lining pipe. Taking the fault slip of 7.5 cm as an example, the deformation of the lining pipe can be reduced by 82% compared with that of the conventional single-layer casing. When the slip amount is small, reducing the wall thickness of the outer tube and the inner tube is conducive to increasing the annular clearance and absorbing the slip amount of the fault, while the effect of reducing the deformation amount of the casing through the annular clearance is not obvious when the slip amount is large. The larger the dip Angle of the fault plane is, the greater the shear stress the lining pipe will bear, and the greater the resulting deformation. Compared with the slip plane inclination of 45° and the dip Angle of 60°, the lining pipe will bear greater shear stress, and the lining pipe is more prone to deformation in this case. The research results can provide reference for casing deformation control in shale gas field.