In the present work, a uniform discharge in low-pressure air was obtained by a dielectric barrier discharge device. The spatial homogeneity of the plasma temperature was studied by optical emission spectrum. The vibrational temperature was calculated by second positive band C3Πu→B3Πg and the rotational temperature (gas temperature) was calculated by N+2 first negative band B2Σ+u→X2Σ+g. It was found that the vibrational temperature decreases with the voltage increasing, while the rotational temperature increases. In addition, the fluctuation amplitudes of vibrational and rotational temperature of the plasma along diameter of the discharge area decrease with the voltage increasing, which indicates that the homogeneity of the plasma increases with the voltage increasing. These results are of great significance to the application of uniform discharge obtained in air dielectric barrier discharge for material processing.