Abstract: This study is based on gas diffusion method, using methane as processing gas to explore the production technology route of high abundance carbon-13 isotopes. Single stage and four stage cascade diffusion separation experiments were conducted, and preliminary cascade calculations were carried out. Under the existing experimental conditions, the maximum total separation coefficient of methane in single-stage experiments reached 1.025, and in four stage cascade experiments, the maximum total separation coefficient reached 1.018. Based on the experimental results, cascade calculation and optimization were carried out, and the product with a carbon-13 abundance of over 90% can be obtained at the heavy fraction end through a three-step cascade of about 600 stages. This study verified the feasibility of using methane gas as processing gas for diffusion separation of carbon isotopes, and provided a technical basis for carbon isotope diffusion separation.