Abstract: The technical difficulties on thermal design, suitability under –195℃ ultra-low temperature condition, analysis and verification of beam pointing error caused by thermal distortion for high gain antenna of Mars orbiter were summarized, and relevant design and verification were completed. Based on thermal design state, the temperature field and thermal distortion of high gain antenna under typical working conditions during the operation on orbit were simulated and analyzed. A vacuum thermal distortion measurement system for large aperture reflector antenna was designed and developed. According to vacuum thermal distortion test data, the beam pointing error was evaluated by a hybrid simulation method. The results show that the maximum beam pointing error is 0.028°, and the gain loss is less than 0.5dB, both of which are within the design margin. The on-orbit test results confirm that the beam pointing performance is consistent with the evaluation, which effectively verifies the accuracy of the thermal design and verification method.