Abstract: The harmonic reducer is one of the important space moving parts, and its operation state directly affects the performance of the whole transmission system. In order to study the service performance of the harmonic reducer in the space environment, a specified simulation test facility is developed to be used for the comprehensive performance testing of the harmonic reducer in vacuum and high-low temperature environments. To reduce the transmission error of the test device system itself, the test bench of the harmonic reducer is placed in the facility chamber, to avoid the use of the magnetic fluid seal shaft and, meanwhile, to shorten the transmission chain. At the same time, a set of temperature control and monitoring systems for the harmonic reducer test bench is outfitted, to withstand the space environmental temperature of -70 ℃ to 150 ℃. The experimental results show that the test facility can meet the design requirements, and provide support for investigating the transmission performance, as well as the working life and reliability test of the spatial transmission mechanisms, and also for the development of such kind of devices.