A method to estimate submarine′s strongly nonlinear motion and hydrodynamic performance during emergency ascent was presented. RANS equations and VOF (volume of fluid) model were applied for simulation cases. The oblique towing experiments with different pitch and yaw angles were calculated numerically to verify the effectiveness of the method and obtain the proper application range for a fully appended Suboff model. Therefore, the emergency ascent process of submarine was simulated with integral dynamic mesh strategy, and the time parameters and the detail flow information of submarine under 6DOF (six degree of freedom) motion were obtained. Numerical simulation results show that the method can reasonably describe the motion law for submarine′s emergency ascent and is feasible and powerful in the research about the multi degree of freedom motions and hydrodynamic characteristics of the submarine′s ascent.