In order to ensure the normal operation of the floating fan in service period, it is necessary to evaluate the long-term limit response of the floating fan platform. Based on the 10-year post-wave data of a certain sea area in Guangdong province, the inverse second-order reliability method is used to select the environmental conditions, and the short-term extreme value calculation of the 5mw-csc floating fan platform is simulated considering the directivity of the environmental load, the long-term limit response of the floating fan platform during the 100-year return period is calculated, and the variation rule of the long-term limit response of the floating fan platform with the angle between wind and wave is studied. The results show that the generalized extremum distribution can be used to describe the short-term distribution of the maximum mooring tension in this sea area, the long-term limit response of the platform is also affected by the wind-wave anisotropy. The effect of wind-wave anisotropy in particular sea area, especially in the sea area with variable wind-wave angles, should be discussed separately.