When a ship encounters an abnormal waves, the instantaneous impact will cause the wave load to change drastically, which may even cause the ship to capsize in serious cases. In order to investigate the special ship type that can effectively resist the impact of freak waves, this paper takes a submerged unmanned ship with excellent adaptability to high-intensity wave loads under extreme sea conditions as the research object, and analyzes its motion characteristics under various wave environments. Firstly, based on the Reynolds-averaged Navier-Stokes equations (RANS), the effects of the fifth-order Stokes waves and freak waves with different wave amplitudes on the water surface motion of the unmanned ship are taken into account; secondly, the motions of the ship's longitudinal rocking and pitching oscillations in the two degrees of freedom are analyzed using the DFBI model; and again, the results of the simulation are visualized to analyze the surface pressure of the hull, the total resistance, the motion response and the load characteristics of the ship. The simulation results are visualized again to analyze the surface pressure, total resistance, motion response and load characteristics. The results show that with the increase of wave amplitude, the wave load of the submerged unmanned ship increases, and the motion response is more violent; compared with the fifth-order Stokes wave, the wave load of the unmanned ship in the deformed wave is smaller, which is better for the safety of the hull structure, because the bow of the submerged unmanned ship combines the advantages of the conical bow and the bulbous nose bow, which can disperse and divide the wave flowing through the bow, and effectively inhibit the impact of the wave. This effectively suppresses the impact of the waves and ensures the safety of the unmanned ship in extreme sea conditions. The results of this study can provide technical support for the safe navigation of submerged bow-type unmanned ship in extreme sea conditions such as freak waves.