The surrounding concrete of steel spiral case in the power station of Three Gorges Project(TGP) is constructed by means of keeping aspecific level of internal pressure during construction. For analyzing the contact behavior of the interface between the steel spiral case and its surrounding concrete，the numerical simulations of the construction process according to the actual construction procedure are carried out with 3-D FEM．The variation of the gap and the interaction force between the steel spiral case and its surrounding concrete in different operation stages and different seasons are put forward. By comparing the? computed results with the prototype safety monitored data during and after the construction of surrounding concrete, it shows that they are in good agreement. The method and the program are proved to be feasible.