In connection with Three Gorges Project, the model of contact between soft layer and inner lining steel tube surface is built by ANSYS, Based on the contact nonlinear and nonlinear cracking, by the non-linear finite element method, the state of stress of steel bar and cracking of concrete are analyzed. The result of calculating indicates:placing soft layer between penstock and concrete can reduce tension stress and improve the anti cracking safety of surrounding concrete, and thoroughly play penstock into full play. The opinions for optimization were put forward finally.