In this paper, a model of activated carbon was established by molecular simulation and the separation performance of N-2 and CH4 on activated carbon was studied. In order to evaluate the adsorption selectivity and diffusion selectivity of N-2 and CH4, Grand Canonical Monte Carlo and molecular dynamic methods were used to obtain equilibrium adsorption isotherms and mean square displacements of N-2 and CH4 on activated carbon with different pore sizes. Research results showed that the difference in adsorption isosteric heat of N-2 and CH4 at the pore size of 0.46 nm is the largest, which is 5.759 and 7.03 kcal.mol(-1) (1 cal-4.184 J), respectively. Activated carbon with pore size of 0.46 nm has the best N-2 and CH4 adsorption selectivity, while its diffusion selectivity is not obvious. (C) 2020 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.