Abstract: The KM5A space environmental simulation test facility is a large-scale facility capable of simulating the spacecraft in-orbit environment of vacuum, cold black and solar radiation in the space for thermal balance and thermal vacuum tests. The equipment is made of a vacuum chamber, a vacuum pumping system, a nitrogen system, data measurement units, and an infrared heat simulator. This paper presents the technical specification, the structure configuration, the key technologies of the KM5A facility.