Abstract: The steam reforming and partial oxidation of methane to produce hydrogen under dielectric barrier discharge were conducted in the CH₄-O₂-N₂-H₂O reaction system; the effects of H₂O/CH₄ molar ratio, O₂/N₂ molar ratio, total gas flow, discharge voltage and discharge frequency on the hydrogen production were investigated and the reaction mechanism was analyzed on the basis of the in-situ diagnostic emission spectroscopy. The results indicate that the conversion of methane and the yield of hydrogen increase with the increase of H₂O/CH₄ molar ratio, O₂/N₂ molar ratio, and discharge voltage, but decrease with the increase of the total gas flow rate and show an volcano-shape trend with the increase of discharge frequency (peaked at 9.8 kHz). Under the conditions with an H₂O/CH₄ molar ratio of 1.82, O₂/N₂ molar ratio of 2.1, total flow rate of 136 mL/min, discharge voltage of 18.6 kV and discharge frequency of 9.8 kHz, in particular, the conversion of methane and the yield of hydrogen reach 47.45% and 21.33%, respectively. During the reaction, methane and water vapor may dissociate by the action of high energy electrons to generate CH_x ·, H·, OH·, O· and other free radicals and hydrogen is then produced through the collision between the free radicals. H· may come from the electronic dissociation of CH₄ as well as the dissociation of OH· formed primarily from the water vapor dissociation. The partial oxidation of methane is mainly manifested by the oxidation of CH₂· with O·, where O· is produced by the electronic dissociation of O₂ as well as the further dissociation of OH·.