Abstract: To improve the conventional refrigeration technology using liquid nitrogen, for a low temperature in thermal vacuum environment simulating test at -80 ℃, the mixed working fluids refrigeration technology is adopted in an environment simulator where thermal shrouds temperature can reach -130 ℃. In this paper, mixed working fluids refrigerator in an environment simulator is designed, and its working flow and performance are described. The results show that the facility can work reliably, and its performance can meet the requirement of thermal vacuum test.