Abstract: With the rise of low-orbit internet satellite constellations and the development of satellite antenna technology, joint wireless testing of satellites and antennas in a thermal vacuum environment has become a new testing mode to increase test coverage. Therefore, it is necessary to establish a comprehensive thermal test environment with high vacuum, low temperature, and low microwave reflectivity. This article analyzes and identifies the key parameters that need attention when applying absorbing materials in vacuum and low-temperature environments and provides reference indicators. The technical process, testing content, and results of the development of a microwave-absorbing heat sink based on carbon foam-absorbing materials with low microwave reflectivity and low passive intermodulation (PIM) indicators are presented.