Abstract: To achieve rapid and precise control of flow parameters in Cryogenic Wind Tunnels, the relationship between the driven-fan power and the wind tunnel operating parameters (such as Mach number, Reynolds number, pressure, and temperature) should be well described. Based on the running pressure ratios and state parameters of a 0.3-Meter Cryogenic Wind Tunnel at CARDC, it is found that the running pressure ratio is approximately linear with Ma²Re_c^−0.095, where Ma and Re_c are respectively the Mach number and the Reynolds number. This model has been further verified theoretically. The running pressure ratios estimated by this model are in good agreement with the experimental results within a wide range of Reynolds numbers at the test section with the Mach number less than 1.0. In addition, this model relates the liquid nitrogen consumption and compressor power with the tunnel operation state in a relatively simple way. Thus its application in the feed-forward control of wind tunnels will simplify the control process, minimize the consumption of the cooling liquid nitrogen, and reduce the stabilizing time considerably.