Abstract: Proposed is a two-pot-two-step simultaneous conversion system for carbon dioxide and a hydrocarbon containing at least one hydroxy group and a method thereof. The system integrates a process of producing a metal salt that is a dehydrogenated form of the hydrocarbon, hydrogen, and water by reacting a hydrocarbon containing at least one hydroxy group in the presence of water and a metal oxalate, and a process of converting carbon dioxide or carbon dioxide-derived carbonate into formate by hydrogenation, thereby increasing energy efficiency while maintaining a higher hydrocarbon conversion rate and a higher carbon dioxide conversion rate than the one-pot conversion system for hydrocarbon and carbon dioxide.