Abstract: Low temperature environment is simulated by using a cascade refrigeration system in the thermal vacuum test facility of spacecraft subassembly. The flowchart and the characteristics of the cascade refrigeration system are given in this paper. Design for a cascade refrigeration system is optimized with respect to the life and reliability of the test facility. The cascade refrigeration system can be applied to the thermal vacuum test facility of spacecraft subassembly, ordinary pressure high and low temperature test container, low temperature box for medicine, and so on.