AbstractModels with different thicknesses of sediment layer were developed based on the finite element method and equivalent‐bodyforce approach. Taking the fault information of the 2013 Lushan County Ms 7.0 earthquake as an example, the co‐seismic deformation of the surface under different thicknesses of sediment layer is comparatively analyzed. It was found that the effect of sediment layer on the co‐seismic deformation is mainly in the vicinity of the fault (‐40km to 40km). The effect of the sediment layer on the co‐seismic deformation in the horizontal direction is greater than in the vertical direction. As the thickness of the sediment layer increases, the horizontal co‐seismic deformation values decrease over most of the area, but increase near the right‐hand endpoint of the fault, and the vertical co‐seismic deformation values gradually decrease. The greatest effect of the sediment layer on the co‐seismic deformation is located in the range of 15km to 20km. For example, when the thickness of the sediment layer is 3 km, the co‐seismic deformation in the horizontal direction increases by a maximum of 90%, and the co‐seismic deformation in the vertical direction decreases by a maximum of 60%. Therefore, the effect of sediment layer on the co‐seismic deformation cannot be ignored.