Aiming at the problem of wasting high-efficiency wavelength bands in the common aperture polarization multiplexing space laser communication optical antennas using beam splitter, a beam splitting structure is designed by using polarizing beam splitting prism and Faraday rotator. According to the parameters of the existing space laser communication device, the requirements for the isolation of beam splitting structure in space laser communication system are analyzed, the isolation and optical loss of the structure are calculated, and the applicable ranges are analyzed. The calculation results show that the structure can be applied to common-aperture polarization multiplexing space laser communication optical system.