Abstract: The high range of the Reynolds number is a core requirement for the aircraft model testing in the wind tunnel, and the feasible engineering way for broadening it is reducing the total temperature of the fluid. Therefore the cryogenic wind tunnel is needed. The mechanical circuit system is the core function facility of the cryogenic wind tunnel with special characteristics as complex structure, high integrated functions, and cyclical loading bearer. By contrasting the design of the overseas the cryogenic wind tunnel and the domestic cryogenic technology, the key technologies for the cryogenic wind tunnel mechanical circuit system design are discussed in this article, such as cryogenic materials, thermal stress and deformation control, wide temperature range and heavy load transmission mechanism, liquid nitrogen spray valves and model transposing for cryogenic testing. The core indicators, technical difficulties and research approaches of each aforementioned key technology are expounded, respectively. Finally, some proposals are offered for the cryogenic wind tunnel mechanical design.