Abstract: It is important to establish the system that is used to evaluate the performance of the inter-satellite laser communication terminals(LCT) under the laboratory conditions before being sent to space. For this reason, beam transmission process of communication was analyzed, and the link simulation based on optical system was also developed in this paper. The relationship between beam transmission and optical magnification with center sampling was studied firstly. Using physical optics principle, the relationship between magnification and transmission distance was established in the next, and on the basis, a system that can be used to test different transmission wavelength and variable transmission distance LCT was designed. Then, the device was tested and calibrated, besides, the relationship between zoom magnification and geometric attenuation was also analyzed. Finally, the precision of transmission distance simulation was discussed. The results indicate that the apparatus can meet less than 100 000 km LCT's simulation with 4% precision of distance simulation and less than 2% stability, which can satisfy the most LCT's testing requirements.