The geostationary earth orbits（GEO） satellite-borne laser communication terminal is of an open-type structure and the laser communication antenna is uncovered out of the satellite. The effective operation time of the antenna is only 4 to 6 hours per day due to the strictly alternate orbital heat flux changing. The solar window is designed to weaken the effect of the orbital heat flux and to improve the thermal stability of the laser communication antenna based on existing thermal control technology, and the optimal design of the optical and thermal properties is obtained by the finite element analysis method as the thermal properties of the laser communication antenna is most stable. The solar window has a larger solar transmission, smaller absorption and larger infrared emissivity for inner and external surfaces. The laser communication antenna secondary mirror can meet the temperature index on whole day and the main mirror can be used for 12 hours per day by utilizing the optimal designed solar window. The effective operation time of the secondary mirror and the main mirror are twice and triple respectively as much as the time of the basic case without the solar window.