Abstract: The numerical analysis of fatigue damage of offshore wind turbine structures is carried out based on the integrated finite element-multibody dynamic model. In order to consider the rotational sampling effect of the blade,a new method proposed recently is adopted. In this method,the joint wavenumber-frequency spectrum is combined with the spatiotemporal transformation so that the wind speed experienced by the rotating blades can be accurately generated. Provided is also an explicit analytical expression of the rotational sampling spectrum,through which the transfer mechanism of the turbulent kinetic energy in the frequency domain is clearly revealed.On this basis,the fatigue damage of offshore wind turbine structures with and without rotational sampling effects is analyzed and compared. The results show that the fatigue damage of wind turbine structures increases significantly due to the rotational sampling effect.