Abstract: Taking the NREL-5 MW offshore wind turbine as an example,the value of cross-wind aerodynamic damping in operational condition was calculated based on the theoretical calculation model and the results were verified by FAST software. Then,the influence of rotor speed,blade-pitch angle and operation mode on the cross-wind aerodynamic damping was studied. The research results show that the cross-wind aerodynamic damping of the NREL-5 MW offshore wind turbine varies from 0% to 0.8% in operational conditions,and it increases with the increase of the rotor speed and blade-pitch angle. In addition,different operation modes of offshore wind turbine will also have an impact on the cross-wind aerodynamic damping.