Abstract: Aerodynamic damping effect has an impact on dynamic responses of an offshore floating wind turbine induced by the greater platform motion of an offshore floating wind turbine, which has attracted increasing attention by Chinese and foreign scholars recently. In order to investigate aerodynamic damping effects on an offshore floating wind turbine, a mathematical model of the aerodynamic damping of offshore floating wind turbines is deduced, and then the study on the characteristics of the aerodynamic damping effect of offshore floating wind turbines and the law of the aerodynamic damping effect of offshore floating wind turbines are conducted using model experimental results and simulation results in the paper. The results show that the aerodynamic damping effect of a semi-submersible offshore floating wind turbine in operation condition is greater than that in parked condition. Aerodynamic damping effect restrains the platform surge motion, the platform pitch motion and the nacelle motion of a semi-submersible offshore floating wind turbine in the operation condition. In frequency-domain, aerodynamic damping effect has an impact on motion at its inherent frequency but has little effect on the motion in wave-energy frequency range relating to the wind speed and wave state. The aerodynamic effect of offshore floating wind turbines is in positive correlation with the wind speed, but the gradient of aerodynamic damping effect of a semi-submersible offshore floating wind turbine gradually decreases with the wind speed below the rated wind speed. When the wind speed reach or exceed the rated wind speed, there could be negative damping effect on an offshore floating wind turbine with a blade-pitch-controller. It is found that decreasing proportionality coefficient of the blade-pitch-controller can reduce the sensitivity of the blade-pitch-controller so as to mitigate the negative aerodynamic damping of a semi-submersible offshore floating wind turbine and improve the motion performances of a semi-submersible offshore floating wind turbine to some extent.