In order to improve the heave performance of floating wind turbine, a heave plate suitable for 5 MW semi-submersible floating wind turbine is designed in this study. Based on model test and numerical simulation, the influence of heave plate on the motion performance of floating wind turbine is studied. In the model test, the natural period and damping of the floating wind turbine system in still water were tested. At the same time, the numerical calculation model of the floating wind turbine system is established to compare and analyze the influence of the heave plate on the motion performance of the floating wind turbine under different working conditions. The results show that the heave plate significantly increases the natural periods of surge, pitch and heave degree of the floating wind turbine and increases the damping of the floating foundation. Therefore, this design effectively suppresses the heave of the floating wind turbine system and reduces the fluctuation of the blade aerodynamic load and the mooring force.