According to the basic principle of laser communication and common aperture technology, the parameters of the optical system of common aperture free space laser communication are analyzed, and an off-axis common aperture laser communication optical system is designed. With an off-axis two-mirror structure, the optical antenna of the system has an effective aperture of 160 mm and the beam compression ratio is 10∶1. Tracking and pointing system adopts non-focus telescope structure. The maximum tracking field of view is ±1 mrad, and the best tracking accuracy is 2 μrad. Based on Zemax software, the ray tracing and performance analysis are given. The results show that the wavefront error of the system is better than 0.1λ (λ=632.8 nm), so the performance of the system is excellent. The system is of the compact structure, the reasonable tolerance and the simple assembly. The system can meet the needs of practical application and has certain engineering significance for the realization of medium earth orbit (MEO) free space laser communication.