In order to investigate the hydrodynamic characteristics of submarines moving in ice regions, a mathematical model and corresponding numerical method, considering the coupling interaction of submarine, water and ice, were established based on RANS equations for level ice and brash ice conditions. The ice sheet was regarded as a no-slip wall boundary with a tangential velocity equal to the incoming flow speed, while the discrete element method incorporated with a linear elastic model was employed to simulate the motion and collision of brash ice. The SUBOFF submarine model was selected as the research object. The influence of sea ice on the resistance was numerically investigated first after mesh convergence analysis. Then further calculations were conducted on resistance components for different submerged depths and speeds under various ice conditions. And wave patterns of the SUBOFF were analyzed for free surface and brash ice condition. Numerical results show that the sea ice predominantly affects the pressure resistance, especially the wave-making component, while there are little differences in frictional resistances for different submerged depths and ice conditions. As the submarine moves under level ice, a significant decrease in pressure resistance and total resistance is observed owing to the lack of wave disturbance. In contrast, when navigating in water covered by brash ice, waves are generated. However, the random and uncertain collisions of floating ice lead to strong fluctuations in the pressure resistance and total resistance curves. And the corresponding average resistance values are slightly smaller than those in open sea due to the wave attenuation induced by brash ice. Furthermore, the submerged depth and forward speed are found to have a significant impact on the hydrodynamic characteristics of the submarine sailing in ice regions. With the increase of submerged depth, both pressure and total resistances will gradually decrease and tend to be consistent. Generally, the increase of forward speed will lead to larger resistance. However, when the submarine navigates beneath the open sea or brash ice, the pressure resistance increases at first and then decreases slightly, which makes the total resistance to grow at a slower rate.