Aiming at the problems of unstable output power and low coupling efficiency of the offshore wind-wave complementary power generation system, this paper proposes a scheme of coupling wind and wave energy using differential gear mechanism. With the power generation of 20Kw as the design goal, the differential gear mechanism in the scheme is designed, and the dynamic equation of the differential gear mechanism is established. The sub-model of the differential gear mechanism is created by using the secondary development platform of AMESim, and the simulation model of wind-wave complementary power generation system is constructed in AMESim. By optimizing and matching the model parameters, the stable power output of the coupled generation system is realized. The average generation power is 18.4kW , the average coupling efficiency is 92%. compared with the independent power generation of the two systems, the efficiency is increased by 7.5%, which provides a new set of solutions for efficient energy coupling of wind-wave complementary power generation system.