In this study, gas temperature measurements of argon, nitrogen, and air microwave plasmas are achieved by the molecular emission spectrometry of the A2Σ+→X2Πr electronic system of OH radical. The gas temperatures at different microwave powers or gas flow rates were explored, and the axial temperature distributions of nitrogen and air microwave plasma plumes were measured. The experimental results showed that temperatures in the core region of microwave plasma were higher than 2000 K at different working conditions, even up to over 6 000 K in air microwave plasma. At the same working condition, the three kinds of microwave plasma gas temperatures meet: ＴＡｒ<ＴＮ２<ＴＡir. The gas temperature increased slightly with the increase of microwave power, and decreased slightly with the decrease of gas flow rate overall. The gas temperatures of nitrogen and air microwave plasma plumes reduced quickly along the axial direction. In order to verify the accuracy of molecular emission spectrometry, the thermocouple was used as a comparison to take the temperature of the dielectric barrier discharge argon plasma. Experiments showed that the temperature measurements of molecular emission spectrometry and thermocouple are fairly consistent.