Abstract: A fully coupled dynamic model was established based on FAST-to-AQWA (F2A). Typical short-term sea conditions in the South China Sea were selected to investigate the platform dynamic response under complex sea states. Fatigue damage of six mooring systems was evaluated using the stress-number of cycles (S-N) and tension-number of cycles (T-N) curve methods. Results show that external loads cause severe surge and sway motions of the platform, and the tension on the windward side mooring lines increases significantly. Increasing mooring physical parameters reduces the platform surge, sway and yaw responses but increases tension. Mooring chain density and strength dominate the surge response, while equivalent diameter and stiffness dominate the sway response. Windward side mooring lines suffer greater fatigue damage, which fluctuates significantly under different sea conditions. The prediction results of the T-N curve method are more conservative than those of the S-N curve method.