The laser communication system with polarized beam splitting is a useful method for interstellar networking. In long-distance communication terminals which adopts a system of common aperture same frequency transmitting-receiving, the stray light comes from the inside system is generated by retroreflectance and scattering, which will cause interference to the reception of signal light. The ability of internal stray light suppression is the main factor restricting the output power of the system signal and the distance of communication chain-establishment. The optical antenna as the key component of the common channel, coaxial optical antennas are replaced by off-axis optical antennas to reduce paraxial stray light. This work designed miniaturized off-axis optical antenna with a large field of view, and combined the YNI factor to analyze the factors affecting the internal stray light. The proportion of stray light generated on each surface was determined through surface modeling and simulation in Tracepro, and the optical antenna was actually tested by constructing optical path. The test result 71dB is close to the simulation result73dB. It indicates that the off-axis angle and YNI factor can be used to characterize the isolation indicator of optical antenna. We believe this work is of great significance for guiding the rapid design and indicator analysis of the system, meanwhile provides reference for other systems of stray light suppression.