Alternating loads induced by complex wave loads are prone to cause load fluctuations and fatigue damage in the main bearing of offshore wind turbines. A single-column offshore wind turbine at a typical offshore wind farm in Yangjiang, Guangdong is adopted as the research object. The dynamic response laws of the main bearing of wind turbines under the complex wind-wave coupling environment are revealed, and the influence mechanisms of multiple environmental factors (e.g., wind speed, wind direction, wave height, spectral peak period) on the dynamic loads and fatigue characteristics of the main bearing are analyzed. First, the structure and working principle of single-column offshore wind turbines are analyzed. Based on the multi-body dynamics theory and in consideration of the load transfer characteristics of single-column offshore wind turbines, a rigid-flexible coupling multi-body dynamics model is established by using the dynamic simulation software SIMPACK. Then, the dynamic responses of the main bearing under the separate actions of different wind and wave conditions and their combined action are systematically calculated, and the influence laws of wind and wave parameters on the dynamic loads of the main bearing of wind turbines are investigated. On this basis, the short-term fatigue damage of the main bearing is quantitatively evaluated in accordance with the Palmgren-Miner linear damage accumulation theory and with reference to the method specified in the ISO 281:2007 standard. The results show that the load and fatigue characteristics of the main bearing are affected by the coupling of multiple environmental factors. Wind speed exerts an influence on the bearing force and operational stability of the main bearing of the wind turbine: when the wind speed increases from 6 m/s to 18 m/s, the bearing force on the main bearing increases gradually with a larger fluctuation amplitude, and the fatigue damage value rises from 17.871×10?? to 58.017×10??, with a relative increase of 224.64%. Under the extreme coherent gust with direction change (ECD) condition caused by sudden wind direction change, the maximum lateral load of the main bearing increases by 15 436% compared with that under the 12 m/s steady wind, and its daily fatigue damage value is 4.05 times that under the 12 m/s steady wind, which significantly accelerates the accumulation of fatigue damage. Waves indirectly amplify the load fluctuation and fatigue damage of the main bearing by inducing tower-top sway: at the turbulent wind speed of 12 m/s, the amplification factor is 1.16 under the action of normal waves and reaches 1.29 under the action of extreme waves. It can be concluded that in the complex marine environment, the dynamic characteristics of wind loads are the main factor inducing the fatigue of the main bearing, while wave loads play an amplifying role, and the increase of wave load level will further aggravate the fatigue damage, which indicates that the wind-wave coupling effect cannot be neglected.