Abstract: he reasons why cryogenic wind tunnels (CWT ) may increase Reynolds number are discussed; the principles and characteristics of high Reynolds aerodynamic test, hot jet simulation test for flight vehicles and high Reynolds number/high Grashof number/high temperature ratio convective heat transfer research by cryogenic wind tunnels are analysed. The results show that cryogenic wind tullnelshave many outstanding advantages when those tests are in comparison with conventional methods and have a lot of meaning for aeronautics and astronautics sciences. The available approaches to construct cryogenic wind tunnels in China are suggested. Finally, some important special key technological problems associated with cryogenic wind tunnels such as working temperature choices, refrigeration and control system, insulation system, wind tunnels model and data measurement are discussed in detail.