The conversion of CH4 with oxygen and steam in a dielectric barrier discharge (DBD) was studied in the paper to discuss the effects of different factors,such as the content of feed-in gas,the applied voltage and frequency.The results showed that a lower ratio of CH4 to O2 always resulted in a higher conversion of CH4.When it was 2,the conversion reached 32.43% without steam introduced into the system.The main effect of steam was increasing the selectivity to CO.The reaction was accelerated and the selectivities to CO and hydrocarbons were enhanced by increasing the applied voltage.It was also observed that a higher frequency led to a lower current and then restrained the reaction.