In view of the difficulties in predicting the underwater motion state of a multimodal amphibious robot caused by complex working environment，a five-degree-of-freedom dynamic and kinematics model for underwater motion of a robot was constructed based on the hydrodynamic coefficient solved by CFD method. Based on the underwater dynamics model of the robot，the fourth order classical Runge-Kutta methods is used to conduct numerical simulation research on the direct sailing motion and horizontal rotation motion of the robot，and pool experiments are carried out for verification. The error between the experimental data and the numerical simulation results is less than 10%，which verifies the accuracy of hydrodynamic coefficient and five-degree-of-freedom dynamic model of the robot，providing reliable theoretical guidance for robot development.
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