Aiming at the problem of inaccurate motion modeling for non-standard ship types, the non-standard underactuated ship is taken as the research object. A three-degree-of freedom motion model of an under-actuated ship was established based on the motion of the ship in still water. STAR-CCM+, the commercial software of CFD is used to simulate various sports conditions of the ship. Subsequently, through the curve fitting and calculation method, the hydrodynamic derivatives of the ship are obtained, and a complete ship motion model is established. Finally, the model was substituted into an existing controller for simulation verification, and the simulation results confirmed the accuracy of the model.