Carbon dioxide reforming of methane to syngas is one of the primary technologies of the new poly-generation energy system on the basis of gasification gas and coke oven gas. A free energy minimization is applied to study the influence of operating parameters (temperature, pressure and methane-to-carbon dioxide ratio) on methane conversion, products distribution, and energy coupling between methane oxidation and carbon dioxide reforming methane. The results show that the methane conversion increases with temperature and decreases with pressure. When the methane-to-carbon dioxide ratio increases, the methane conversion drops but the H2/CO ratio increases. By the introduction of oxygen, an energy balance in the process of the carbon dioxide reforming methane and oxidation can be realized, and the CO/H2 ratio can be adjusted as well without water-gas shift reaction for Fischer-Tropsch or methanol synthesis.