Proposed is a carbon dioxide conversion system and method. More particularly, proposed is an eco-friendly carbon dioxide conversion system and method, the system and the method returning, in the recycling of Fischer-Tropsch synthesis reaction off-gas, a part of the off-gas to a Fischer-Tropsch reactor and producing a synthetic natural gas through methanation of the remainder of the off-gas, thereby improving overall energy efficiency and carbon efficiency, and thus a useful hydrocarbon fuel is produced from carbon dioxide, thereby providing a carbon dioxide-reducing effect.