This paper reports it reduced mechanism used in Urea-based SNCR process for NO, 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 Lit 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 O-2 and CO concentrations. The performances of QSS graph method and traditional QSSA by iteration are compared in plug-flow computations. The deviation in accuracy is only in order of 0.01%, while QSS graph creates nearly 40% speed-up significantly superior to QSSA by iteration.