This paper reports a reduced mechanism used in urea-based SNCR process for NOx control that is developed from the detailed mechanism originally proposed by Rota et al. (Chem. Eng. Sci. 2002, 57, 27−38) consisting of 173 elemental reactions and 31 chemical species. Sensitivity analysis and rate-of-production analysis are first conducted to exclude redundant elemental reactions and species, forming a skeletal mechanism. After that, quasi-steady-state species are identified and a 12-step 16-species reduced mechanism is established. The balance equations for quasi-steady-state species are innovatively solved by means of QSS graph method presented by Lu and Law (J. Phys. Chem. A 2006, 110, 13202−13208) with the avoidance of efficiency compromise stemming from algebraic iterations. The predictions of the reduced mechanism show satisfactory agreement with those of the detailed one over a wide range of operating conditions, including various temperatures, molar ratio of CO(NH2)2/NO and O2 and CO concentrations. T...