Based on FAST, the time domain model of OOstar platform is established, and the response of the platform under the wind and wave actions are investigated. The distribution of random motion of the platform is analyzed by statistic method, and the spectra of platform motion are calculated by Fourier transform, especially focusing on the impact of wave difference frequency force and wind load on the low frequency slow drift motion. The results indicate that: the wave difference frequency force and wind load will increase the amplitude of the platform, and strengthen the discreteness of periods related to big-amplitude motion, while are of little influence on the periods corresponded to small-amplitude motion; the influences of difference frequency force on the amplitude and period increase as the wave states getting worse, while the influences of wind loads are opposite. The spectrum analysis indicates that the difference frequency force stimulates the platform response at its natural frequency under different sea conditions, while the influence of wind load is obvious only at the fourth wave state.