Methane (CH4) and carbon dioxide (CO2), the main components of biomass pyrolysis gasification gas and biogas, are byproduct gases that can be used as energy sources and are also greenhouse gases that contribute to global warming. This study on microwave reforming characteristics was conducted to convert the product gas into high-quality fuel energy. In the case of microwave reforming through carbon receptor application, the carbon was generated by a thermal decomposition, and then it attached on the surface of the receptor, interfering with the catalytic activity. Carbon dioxide reforming, however, cleaned the adsorbed carbon through carbon gasification and thus consistently maintained constant reforming conversion. Therefore, when the mixture of methane and carbon dioxide was reformed at the same time, the catalytic activity could be prevented from deteriorating because of carbon adsorption. When sludge char was used in this study as carbon receptor, the amount of hydrogen and carbon monoxide generated was higher than that generated by the commercial activated carbon receptor because of the former's relatively high catalytic activity, yielding a gas product with higher heating value. It was also confirmed that the conversion and the product gas yield were high when the receptor bed reforming temperature was high and when the retention time was long.