Abstract: The unsynchronization of optical satellite communication leads to error information and demodulation difficulty. And carrier frequency offset has effect on frame synchronization of sliding correlation algorithm. To solve the problem, frequency offset caused by satellite Doppler effects was analyzed by calculation simulation and difference relation algorithm was proposed for the realization of frame synchronization and frequency offset estimation. Implementation scheme of hardware was given. The performance of difference relation algorithm was analyzed. The results show that difference relation algorithm implements frame synchronization under the influence of high carrier frequency offset and has strong ability of frequency offset estimation. After using difference correlation algorithm, the error bit performance of the system increases nearly 3dB. It is useful to use difference relation algorithm to solve the synchronization problem of laser satellite link.