A thermochemical nonequilibrium analysis was performed under the low enthalpy shock-tunnel flows. A quasi-one-dimensional flow calculation was employed by dividing the flow calculations into two parts, for the shock-tube and the Mach 6 nozzle. To describe the thermochemical nonequilibrium of the low enthalpy shock-tunnel flows, a three-temperature model is proposed. The three-temperature model treats the vibrational nonequilibrium of O-2 and NO separately from the single nonequilibrium energy mode of the previous two-temperature model. In the three-temperature model, electron-electronic energies and vibrational energy of N-2 are grouped as one energy mode, and vibrational energies of O-2, O-2(+), and NO are grouped as another energy mode. The results for the shock-tunnel flows calculated using the three-temperature model were then compared with existing experimental data and the results obtained from one- and two-temperature models, for various operating conditions of the K1 shock-tunnel facility. The results of the thermochemical nonequilibrium analysis of the low enthalpy shock-tunnel flows suggest that the nonequilibrium characteristics of N-2 and O-2 need to be treated separately. The vibrational relaxation of O-2 is much faster than that of N-2 in low enthalpy condition, and the dissociation rate of O-2 is manly influenced by the species vibrational temperature of O-2. The proposed three-temperature model is able to describe the thermochemical nonequilibrium characteristics of N(2)and O-2 behind the incident and reflected shock waves, and the rapid vibrational freezing of N-2 in nozzle expanding flows.