Since the spiral case of No.15 turbine unit of TGP Hydroelectric Power Station was embedded in concrete directly, the emphasis of research were to obtain a rational reinforcement project and structural measures to guarantee the security of structure. The structures with different reinforcement projects and structural measures were analyzed by three dimensional nonlinear finite element method. The distribution and width of concrete cracks, the stress of steel plate and reinforcement, the displacement of structure and the effect of different structure measures were studied. The results showed that increasing the quantity of reinforcement only is not able to hold back the penetrative cracks of the structure and reduces the asymmetrically rising displacement, and that both extending the length of cushion and enhancing the concrete grade in certain position will lead to reducing the cracking regions, decreasing the crack width and depressing the rising displacement of base plate effectively, furthermore, enhancing the strength of concrete in certain position exceeds adding a layer of reinforcement.