Compared with the fiber channel, the changes of polarization state and the channel characteristics of the two polarization states are relatively slowly in space optical communication channel. At the same time, there have no serious PMD effect in the atmosphere. Because of the relative stability of polarization states in space optical communication systems, we propose and experimentally validate a method that performs low-speed polarization de- multiplexing processing first, and then performs low-speed linear channel equalization for each polarization channel in the DSP process. While the polarization de-multiplexing is realized by ICC algorithm, and the channel equalization is realized by CMA. What’s more, the tap coefficients of ICC algorithm and CMA are able to update by processing the received information sequence in low speed with low-speed logic cells in this method. Therefore, the advantage of this method is that the logic resource consumption in hardware implementation will be reduced by reuse of the low-speed logic cells during FPGA processing while the ICC algorithm and CMA are running. In order to verify the effectiveness of the scheme, we build a communication system that 20-GBd PM-QPSK signals are sent at the transmit-side, and a coherent receiver with local oscillator at the receive-side. By analyzing the constellation diagram and comparing the BER after the ICC algorithm and CMA processing with that after CMA processing, we know that this method simplifies the DSP effectively without significant impact on communication quality.