A relatively precise kinetic mechanism of NOx reduction using N2H4H2O in a selective non-catalytic reduction process was proposed and verified by experiment in this study. The dominant radicals and reactions were confirmed, and the proper ranges of key parameters were determined through sensitivity analysis. Both experimental and simulation results show that the effective temperatures exhibit a bimodal distribution with the optimum temperatures being approximately 893 and 1248 K and the lower temperature window falling in the range of 848-973 K. The optimum residence time of the reaction was 0.2-0.35 s under the research conditions, and a longer residence time would lead to the regeneration of NOx. The normalized stoichiometric ratio (NSR) of 3.0 corresponded to the lowest temperature window, and a higher NSR value would make the temperature window shift to a higher temperature range. This kinetic mechanism model for the N2H4H2O-based De-NOx process will serve its precise application. (c) 2014 American Institute of Chemical Engineers AIChE J, 61: 904-912, 2015