Based on FAST, establishing the time domain model of OOstar platform, the response of the platform under the wind and wave actions are investigated. The distribution of random motion is discussed in statistic method, the spectrum of platform motion are calculated by Fourier transform, especially focusing on the low frequency slow drift motion. The result indicates that wave difference frequency force and wind loads will increase the amplitude of platform, and strengthen the discreteness of periods related to big-amplitude motion, while have little influences on periods corresponded to small-amplitude motion. The influences of difference frequency on amplitude will increase as the wave states getting worse while wind loads are opposite. The spectrum analysis indicates that difference frequency will stimulate the platform response at its natural frequency, while the influences of wind loads is obvious only at fourth wave state.