Abstract: The performance of the propeller attached at the stern of the submarine navigating under limited depths is affected obviously by the free-surface, duo to the changes of the flow field characteristics around this vehicle. And what mentioned above will greatly threaten the security of the maneuverability of the submarine. To figure out the effect of the free-surface on the performance of the propeller attached at the stern of the submarine. In this paper, the URANS (unsteady Reynold average Navier−Stokes) equations coupled with k - \omega turbulence model are used for the numerical simulations about performance of the self-propulsion model (the standard Sub-off geometry and the E1619 propeller). At first, the experimental data available including the resistance tests of the submarine with all appendages under total submergence, the resistance tests of the revolution with different navigating depths and the OWC (open water curve) of the propeller, is used for the validation of the numerical method adopted in this paper. Next, the correctness of the numerical method is acquired based on three sets of grids with different spatial resolutions. Finally, the performance of the self-propulsion model navigating under two depths and three different velocities is simulated carefully to figure out the effect of the free-surface on the performance of the self-model. The numerical results show that the exitance of the free surface increases the rotational speed of the propeller at a specific navigating speed, which corresponds to the self-propulsion point. The increment mentioned above is related to the wave pattern induced by the submarine. The wave pattern will cause the nozzle-like flow between submarine and free-surface. The nozzle-like flow and the suction of the propeller change the angle of attack of the blade profile at different radial sections. Meanwhile, approaching and getting away from free surface will also significantly change the hydrodynamic loads of the propeller.