In order to improve the separation performance of CO2/CH4 on carbon molecular sieves (CMS), CMS was modified by metal in this study. The surface of CMS had-OH, which could provide a great support for the chemical modification. In this paper, different metal ions, precursors of potassium, loading concentration of potassium carbonate (K2CO3), and calcination temperature were investigated for CO2/CH4 separation. Results showed that CMS loaded with K2CO3 and calcined at 773-873 K was the best for CO2/CH4 separation. Compared with the untreated CMS, the adsorption capacity of CO2 for the best adsorbent increased from 1.15 to 1.72 mmol.g(-1) and the value of separation factor increased from 1.9 to 2.75 mmol.Cl. The K2CO3 treatment was effective in generating metal oxide K2O and KO2, which could facilitate the adsorption of CO2 after K2CO3/CMS being calcined. However, the reaction between CH4 and metal was weak. In summary, K2CO3/CMS was proved to be one of the candidates for CO2/CH4 separation.