Abstract: The flat-panel SAR antenna carried by AS-01 satellite has a total heat load density of up to 720 W/m². During the antenna operation, the temperature of the active equipment is required to be in the range of -20 ℃ to 50 ℃, and the temperature difference of the whole array does not exceed 12 ℃. In this regard, a lightweight thermal control scheme based on heat conduction and temperature homogenization was proposed. According to the principle of quasi-passive thermal control design, the array thermal control coating with absorption-to-emission ratio of η=1.4 and multi-layer insulation measures were selected to achieve the desired temperature range. The double-sided installed thermal pads and phase-change heat pipes were applied to enhance the uniform thermal conductivity of the antenna. Active thermal control assistant design for extreme low temperatures was added. Simulation analysis and full-sized thermal balance test on the thermal control were carried out to verify the validity and correctness of the proposed thermal control measures. The final on-orbit flight experiment shows that the average temperature of the antenna is approximately 10 ℃, and the temperature difference across the whole array of T/R module is not more than 8.9 ℃, indicating that the antenna’s thermal control system works stably in orbit.