In this paper, adsorption of methane in actived carbon pores has been simulated by using the grand canonical ensemble Monte Carlo (GCMC) method. In the simulation, Lennard-Jones (LJ) potential is used for represent the fluid-fluid interaction, and the 10-4-3 potential is used for represent the interaction between fluid molecules and a slit carbon wall. Firstly, the adsorption isotherms of methane in actived carbon pores and local density profiles of methane in slit pore are obtained. Then, the interaction energy of methane in slit carbon pores with nine different pore sizes is obtained. Finally, the temperature, pressures, pore sizes affect the adsorption amount was studied, respectively.