Abstract: In the existing simulations of torpedo turbine in non-design condition, a data fitting method was adopted in calculating inner efficiency of a torpedo turbine. We establish a set of models of inner efficiency in non-design condition for the turbine by combining theoretical analysis and empirical formula, perform a simulation, and obtain the variations of inner efficiency and the factors affecting inner efficiency. Simulation results show that the velocity coefficients of nozzle and working vanes are the key factors influencing inner efficiency. Comparison between simulation and test data verifies correctness of the proposed models.