Abstract: Aiming at the design problem of inclined borehole wall in expansive mudstone formation in eastern Mongolia, a theoretical model of circular borehole wall under the combined action of uneven ground pressure and expansive contact pressure is established based on elastic mechanics theory. The analytical solution of borehole stress and displacement under the combined action of uneven ground pressure and expansive contact pressure is obtained. The influence of wall thickness on wall stress and displacement is studied. Based on the thermal coupling module of FLAC^3D, the optimization scheme of different shaft thickness is simulated, and more reasonable supporting parameters are determined by optimizing shaft section and supporting form. The numerical results show that when the outer shaft wall reaches 600 mm and the inner shaft wall reaches 600 mm, the influence of increasing the shaft wall thickness on the displacement and deformation is not obvious. The optimized support scheme can effectively resist wellbore deformation in expansive mudstone formation.