Abstract: In this paper, a 3D nonlinear FEM is used to analyze an embedded spiral casing structure with different thicknesses of spiral steel lining. The results show that even if the thickness of steel spiral case is reduced, its von mises stress or the tensile stress and cracked area of its surrounding concrete does not increase significantly. Even in load rejection condition, after thinning the spiral steel lining, its maximum stress is still less than the yield strength, reaching only one-fifth of the latter, far from its ultimate bearing capacity. This paper also analyzes the spiral structure under overloading and obtains a process of crack initiation and propagation in the surrounding concrete.