Based on the numerical simulation software FINE/Marine of viscous flow theory, the pure heave, pure sway, pure bow and pure surge motions of the robot body at different time periods are solved, and the vertical force, transverse force (moment), bow force (moment) and longitudinal force of the Remote Operated Vehicle (Remote Operated Vehicle, ROV) are obtained. Based on the MATLAB software platform, the system identification method is used to determine the linear hydrodynamic derivatives of four degrees of freedom, which are substituted into the motion mathematical model to complete the rotary motion prediction of the complex underwater robot.