Abstract: According to the companion relationship between marine wind and wave resources, it is extremely feasible to harvest wind and wave energy simultaneously. Based on this, a novel combined wind-wave energy harvesting system with a semi-submersible wind turbine and point absorption wave energy converter（WEC） is proposed. A fully-coupled wind-wave-multi body time domain analysis model considering equivalent PTO（power take-off） is developed in this work. The influence law of wave energy converter parameters on power performance is investigated, focusing on the structural dynamic response characteristics and energy acquisition characteristics of the novel system under a hybrid wind-wave operation sea state. The results show that the installation of the wave energy converter adversely affects the surge motion of the semi-submersible platform and the mooring lines, but has less impact on the wind turbine. In addition, both the heave and pitch responses of the platform are suppressed with the addition of the wave energy converter, the average pitch angle is reduced by 25%, the standard deviation of the heave motion is reduced by 42%, and the average power of the combined system is increased by 17% compared with the single floating wind turbine.