Abstract: This system is an accessory system for vacuum thermal test of satellite, which is used to make a real-time compensation for level errors of the satellite supporting frame due to the large temperature difference and to avoid the failure of heat pipes. The system is constructed based on Siemens S7-300 PLC and Intellution iFIX3.0 industrial automation software. As a console computer, PLC deals with the parameters of level angle and controls the level adjustment. In the master computer, the software system of iFIX controls the system’s processes, acquires and handles the system’s information, and realizes the communication between man and machines. The problems of temperature maintenance of important facilities and of restraining heat exchange are solved in the level control system. The thermal test results show that the heat pipe’s level error due to the large temperature difference is well compensated by using the level control system, which ensures the success of the satellite’s thermal test.