Low temperature conversion of CH(4) and CO(2) was investigated in a coaxial dielectric barrier discharge reactor at ambient pressure. Main parameters, including the input power, the residence time, the discharge gap, the molar ratio of the feed gases and the multi-stage ionization design were evaluated to understand the ways to improve the conversion of greenhouse gases and reduce the output of by-products. At certain input power, the conversion of CH(4) and CO(2) can reach 0.797 and 0.527, respectively, when the molar ratio of CH(4)/CO(2) is one. When this ratio was low to 1:5, the conversion of CH(4) was promoted to 0.843 and the selectivity to CO and H(2) was almost 100%. The multi-stage ionization favored the conversion of CO(2), which would also be an efficient design to promote the selectivity to the main products such as CO and H(2) and suppress the selectivity to the by-products.