Dual time step method is introduced into the calculation of 3D unsteady stator/rotor interaction. The algorithm for inner boundary condition is presented in detail, Following the method, the numerical stability and order on inner boundary could be guaranteed to be the same as those at the internal nodes and the flux also could be kept conservative. Typical unsteady flow pattern about turbine stage with bowed stator is obtained. The numerical cases show that the method adopted in the paper is reasonable.