A series of activated carbon were prepared, modified, and characterized by FTIR, Boehm titration, and N-2 adsorption/desorption isotherms. Adsorption breakthrough experiments of CH4 through low-concentration coal bed methane (CBM) were carried out for measuring adsorption capacities (Q(m)) of adsorbents toward CH4 at 293 K. Adsorption isotherms of CH4, N-2, and O-2 were measured between 25 mm Hg and 760 mm Hg at 293 K and fitted by Langmuir model to calculate separation coefficient of CH4 against N-2 and O-2 (alpha(CH4/N2) and alpha(CH4/O2)). Results show that CH4 adsorption occurs mainly at the micropore of activate carbon, and the surface basic group of activate carbon can strengthen its adsorption ability toward CH4. Adsorption capacities of CH4 on modified AC are higher than that on original AC. The adsorbent KCl/AC has the largest micropore volume and more amount of basic group and this makes it the largest uptake of CH4 (7.89 mL/g) at 293 K and 1 atm; it is 38.9% higher than that of original AC (5.68 mL/g). Separation coefficient of alpha(CH4/N2), on KCl/AC is 5.33, compared to 3.85 for AC; it is 38.4% higher than that of the original AC.