To enhance plasma applications’ effect, plasma’s discharge kinetic process must be explored in depth. The rotation temperature is one of the important parameters reflecting the energy transport in the plasma discharge process, which is mainly calculated by the Boltzmann slope method, which is commonly used to calculate the rotation temperature of the plasma in the thermodynamic equilibrium state and has a large error in calculating the rotation temperature of the plasma in the non-thermal equilibrium state. To address this problem, this thesis proposes an analytical method to calculate the rotation temperature using diatomic molecular spectral bands. A needle-ring electrode plasma jet device is used for the experiment, and a plasma jet is formed by discharging a mixture of Ar/Air/CH₄ gas into the device with an operating voltage of 10~14 kV. A spectrometer collects the spectral data of the plasma jet at different discharge voltages to calculate the rotation temperature. The OH (A—X), CH (A—X) and emission spectra were selected to investigate the rotation temperature of the Ar/Air/CH₄ plasma jet, using the property that the spectral lines in the wavelength interval of the three diatomic molecules, are not affected by the change of vibration temperature. The rotation temperature of the DBD-excited Ar/Air/CH₄ plasma jet was obtained by selecting one spectral line every 20 K in the range of ±100 K calculated by the Boltzmann slope method, fitting it to the experimental spectral line, calculating the root-mean-square error obtained from the fit of the spectral line, and analyzing the accuracy of the fit. The root-mean-square error of the rotation temperature, calculated by the Boltzmann slope method obtained in the fit, is higher than the minimum root-mean-square error, and the root-mean-square error can be reduced by 38%. The minimum root-mean-square errors obtained by fitting the OH, CH, and spectral bands were 4.6, 2.9, and 2.1, respectively, and the results of fitting the band were 61% lower than the results of fitting the OH band. The results show that calculating the root-mean-square error of spectral line fitting can effectively improve the accuracy of the calculation results, compared with the Boltzmann slope method when calculating the rotation temperature of the plasma in the non-thermal equilibrium state. The accuracy of the calculation results can be further improved by choosing the emission spectrum of the band for fitting to the experimental spectral line.