Abstract: Space simulator is a large-scale ground test facility used to simulate the satellite environment of vacuum, cold-black and solar radiation in the space in order to carry out the thermal balance and thermal vacuum tests for the development of the satellite. The composition, simulation technology, debugging and service conditions of the space simulator KM3B with an effective test volume of φ3 700 mm×4 800 mm are presented, which is developed by Beijing Institute of Spacecraft Environment Engineering. The results show that the systems of the facility work reliably and the performances of the vacuum, contamination, sink temperature, infrared heat simulator and temperature measurement system can meet the requirements of the vacuum thermal test.