Coal-based carbon molecular sieves (CMS) were modified by organic reagents with affinities for hydrocarbons including tetracosane (C24), lauryl sodium sulfate (SDS), and polyethylene imine (PEI), and low temperature plasma treatment in a CH4 and N-2 atmosphere, respectively. The modified CMS samples were characterized by FT-IR analysis, low-temperature N-2 adsorption tests and SEM. In addition, the adsorption capacities of pure CH4 and N-2 were measured by the static volume method and the CH4/N-2 separation coefficients of the modified samples were also compared. The saturated adsorption capacities q(m) after modification and separation coefficients were investigated. CH4 was more strongly adsorbed on all the modified samples. The sample of CMS-P-N has the best modification effect and its saturated adsorption capacities q(m) were 6.76 mmol/g for CH4 and 5.56 mmol/g for N-2, respectively. The separation coefficient of CH4/N-2 of CMS-P-N was 3.32. Besides, CH4 breakthrough tests were performed using a fixed bed apparatus. The breakthrough curves confirmed that low temperature plasma treatment of CMS in an N-2 atmosphere was beneficial for the adsorption separation of CH4/N-2.