Abstract: An innovative Thermal Environmental Simulation System (TESS) of reliability demonstration for testing large-scale space deployable mechanisms is developed and investigated experimentally. While maintaining the stable thermal boundary conditions, the TESS's insulation chamber structure can adapt to a large temperature difference between the high and the low temperature environments, with two independent inner and outer frameworks connected by insulating glass fiber reinforced plastics in key nodes. A reasonable airflow distribution design ensures an excellent temperature uniformity of high and low temperature environments. The stable heat and cold source supply system can provide enough energy to achieve the target thermal environment. The dry nitrogen replacement system is established to obtain an ultra-low dew point temperature. The measurement and control system based on the PLC is adopted. Experimental results show that the temperature range, the temperature change rate, the temperature uniformity and the dew point of the TESS can meet the testing requirements totally and admirably.