Semi-coke-based activated carbons (SACs) were prepared using semi-coke powders as raw materials. They were modified by organic reagents (benzene, methyl benzoate, and ethyl acetate), low-temperature plasma (CH4 and N-2 atmosphere), and organic reagent-low temperature plasma synergistic methods. FT-IR analysis showed that the corresponding functional groups were introduced to the surface of the SACs and the absorption peak intensities of the corresponding functional groups were enhanced via low-temperature plasma treatment. Low-temperature N-2 adsorption tests showed that the organic reagent played an important role for regulated mesopores of the SACs. The adsorption capacities of the SACs for CH4 and N-2 were measured via static volumetric method, and their separation factors of the CH4/N-2 were calculated, in which the biggest separation factor (5.08) of CH4/N-2 was obtained from the SAC-ben-P-N-2, which was synergistic modified by benzene and lowtemperature plasma (N-2 atmosphere) and its breakthrough time of methane was 93 s. The biggest breakthrough time of methane (112 s) was acquired from the SAC-ben, which was modified by benzene and its separation factor of CH4/N-2 was 4.87. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.