Abstract: The Beijing-3 satellite features complex mission modes, high electronic device integration, and significant power consumption. Enhancing the effectiveness of external heat flux simulation and ensuring efficient completion of the entire satellite thermal vacuum test is crucial for the test design. Based on the analysis of the thermal control design and operational characteristics of the onboard equipment for the Beijing-3 satellite, a temperature control method involving the coordinated adjustment of the infrared cage and internal heat sources through regulating the onboard heating circuit status and setting the operating modes of onboard equipment, was proposed. The thermal vacuum test results show that the onboard equipment temperatures were effectively controlled, all within the acceptance-level test temperature limits, maintaining good temperature consistency across the four cycles. This method has effectively verified the operational capabilities of the satellite equipment under thermal vacuum conditions, offering experience and a reference for future thermal vacuum tests of similar satellites.