Optical emission spectroscopy (OES) was adopted for the first time by our group for in situ diagnosis of the conversion of CH4-H2 under glow discharge plasma at atmospheric pressure with rotary electrodes. The emission of excited species such as excited radicals and atoms (C, CH, C2, H and H2) was detected in the spectra range of 300-700 nm. The spectrum of hydrogen atom was used to figure out the plasma excitation temperature by a Boltzmann plot scheme. It was evaluated that the excitation temperature of hydrogen plasmas under varied discharge conditions is in the range of 6 300-6 600 K. The electron density was calculated based on spectral profile of H lines and its order is about 1020 m-3.