Abstract: It is widely used in the light-isotopes enrichment by distillation, such as H₂, O₂, N₂, CO, etc. It can not get high abundance of isotopes in the late stage of enrichment for these two-atom include two isotopes, and it needs to add a reaction conversion device in the distillation column to remove the interference. By the catalyst, the single isotope gas was obtained from the reaction between the gas molecules, and then continue to separate them to get the high abundances of isotopes. The gas reaction and the catalyst method were introduced briefly. In addition, the equilibrium constant and the reaction mechanism of C isotope exchange reaction were introduced emphatically.