Carbon materials have shown excellent low temperature denitrification characteristic in the flue gas. To improve the denitrification efficiency, metallurgical coke, biomass char and semi-coke were modified by steam or acid. Taguchi experimental design was used to determine the influence of carbon material type, modified time and process temperature etc. on the denitrification rates. Three carbon materials before and after modification were characterized by SEM, BET and FTIR. The results showed that a large amount of specific surface area and smaller pore size were beneficial for NOX removal with NH3, but the surface acidic functional groups were crucial for denitrification. For steam modification, the optimal promotion of denitrification rate was semi-coke, modified by steam at 973 K for 140 min and the nitrogen oxides removal rate was 16.0%. For acid modification, the optimal combination was biomass char, with the deashing acid treatment before oxidation acid treatment at 353 K and the nitrogen oxides removal rate was 24.0%. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.