Carbon dioxide (CO2) conversion technology has been estimated as a potentially practical solution for global warming problems although it still has some weaknesses such as cost and energy consumption. In this study, a combined steam reforming process with dry methane reforming process for the CO2 treatment was investigated. Because the dry methane reforming process could generate synthesis gas from carbon dioxide, it could decrease the CO2 emissions from the existing steam reforming process. Models for the steam reforming process and the combined process were developed and extended mitigation cost was suggested to evaluate CO2 reduction of the overall process. The combined process could reduce net CO2 emission by 67% compared with the reference steam reforming process, and the extended mitigation cost of the combined process ranged from 21 to 26.5 (US$/CO2 ton) according to the change of the cost for CO2 transportation.