Homodyne detection is the main detection method in satellite coherent optical communication,and OPLL is used to eliminate the frequency shift caused by Doppler frequency shift and laser linewidth.But the realization of OPLL is still difficult,and the frequency capture time is too long.The open-loop frequency estimation and phase estimation theory based on DSP were applied to communications between satellites,and the demodulation with 500MHz frequency offset was achieved.Also,combining the merits of EDFA and coherent detection,the received signal was preamplified by using EDFA to improve the sensitivity of the receiver.The simulation results show that the standard-deviation of estimated frequency is less than 8MHz when signal-noise-ration is higher than 7dB,and after adding EDFA,the BER is better than 10-3 when the power of received light is higher than -57 dBm.