Abstract: Space optical communications terminals frequently rely on optical telescopes to enhance the transmitted and received efficiency of the communication system. An optical design of a space laser communications optical antenna system was proposed to overcome the traditional on-axis Cassegrain optical antenna's disadvantages of small field of view and low emission efficiency. As an example, an optical antenna system operating at 0.85 m, 1.064 m and 1.55 m with aperture size 150 mm, magnification 15 was designed. The initial parameters were computed, and the ray tracing and optimization for the optical antenna system were performed with ZEMAX-EE software. The analysis results demonstrate that the Root Mean square(RMS) of a spot radius is less than 10 rad in the working wavelength(0.85 m, 1.064 m, 1.55 m), which implements astigmatism correction and obtains a good diffraction-limited quality in a wide spectral region and a high magnification. These results prove the feasibility of the optical design method proposed.