Abstract: The reaction mechanism of homogeneous and char-catalyzed heterogeneous NO reduction with HCN were investigated by density functional theory (DFT) of quantum chemistry; the reaction kinetic parameters were determined according to classical transition state theory (TST). The results indicate that the activation energy of homogeneous NO reduction is 306 kJ/mol, much higher than that of heterogeneously catalytic reduction of NO; the later can be as low as 136 kJ/mol. Under the typical reburning temperature (1 400 K), the reaction rate of heterogeneous reduction of NO with HCN is slightly lower than that of heterogeneous reduction catalyzed by char; in comparison with the heterogeneous NO reduction by CO, the heterogeneous NO reduction by HCN over char is more likely to occur. The adsorption sequence of various components has a significant effect on the heterogeneous NO reduction by HCN; the reaction rate coefficient of NO adsorbed on char surface with HCN is 5.28×10¹⁰, which is an order larger than that of the surface adsorbed HCN with NO. Char exhibits a significant catalytic effect on the NO reduction with HCN; char provides surface reaction sites for NO reduction which can effectively activate the reaction gas.