Abstract：The study of mantle-derived CO2 is one of the frontiers in Earth science and is hence of great significance. Mantle fluids in supercritical state possess high dissolving and diffusing capacity and serve as an important transporting carrier of energy in Earth’s interior, with their chemical composition being mainly H2O and CO2. Many scholars believe that mantle fluids play an important role in the ore-forming process, but research on their relation with the CO2 gas pool is very insufficient. Along with the magma rising, the relatively insoluble CO2 gas will be the first to release with the temperature and pressure reduction of the magma, and the favorable tectonic environment is likely to form the CO2 gas pool. Many of the world's regional magmatic activities and fractures have formed CO2 gas reservoirs. This paper analyzed properties and influencing factors of mantle fluids exemplified by the study of magma and fault characteristics of Bohai Bay basin in eastern China, and discussed the ascent and evolution process of mantle fluids. The authors believe that mantle degassing may be the main material source of CO2, and that fault activities provide passageways and space for magma uprising and gas migration and accumulation. The favorable sites in search for potential CO2 gas pools lie in magmatic activities on basin margin and intersections of faults of different directions.