The present application belongs to the field of environmental protection, and in particular to a system and method for simultaneously producing high-purity liquid nitrogen and high-purity liquid carbon dioxide at low cost by using flue gas. The system provided by the present application comprises a flue gas boosting and cooling system, a CO.sub.2/N.sub.2 front-end separation system, a liquid CO.sub.2 preparation system and a high-purity liquid nitrogen preparation system The present application can maximize the use of flue gas to produce high-purity liquid nitrogen and liquid CO.sub.2 at low cost, and realize the synchronous resource utilization of carbon/nitrogen components.