根据星地大容量通信发展需求，研究了基于微波空间光传输技术的星地激光通信链路。在建立星地微波光传输链路模型的基础上，分析了链路光功率衰减、输出微波信号、噪声功率以及在大气湍流信道下系统的误码率。仿真分析了调制器直流偏置电压大小对链路输出信噪比和误码率的影响，结果表明，相对于通常的正交偏置工作点，通过优化控制直流偏置点的位置，可以提高链路输出信噪比和误码率，这种改善程度随着调制系数的减小而增大。该研究为建立星地微波光传输系统提供了有益参考。

The radio on free space optical transmission (RoFSO) link is proposed to meet with the large capacity requirement of satellite-to-ground communication. With the established link model, the link optical loss, the output power of microwave signal, noise and the bit error rate (BER) under atmospheric turbulence channel are deduced. The influence of bias voltage of the electro-optic modulator on the signal to noise ratio (SNR) and BER is simulated. The analysis results show that compared with the quadrature bias point, the optimal control of the bias voltage can improve the SNR and BER. And the effect of improvement increases with the decrease of the modulation coefficient. The research gives good foundation for the realization of RoFSO based satellite-to-ground communication system.