This work employs large-scale simulations of reactive molecular dynamics to investigate influences of coal char structures, O 2 concentration, and temperature on NO x formation during coal char oxidation processes, which are facilitated by combining high-performance computing and cheminformatics-based reaction analysis. The char property models are constructed by using a new strategy on the basis of nascent structures taken from different pyrolysis stages individually from a large coal model. Analysis results of the char model structures show that nitrogen atoms would transform into N-containing six-membered ring groups from coal to a matured char structure at the high temperature of the late pyrolysis stage. Analysis of the simulation trajectories reveals that fuel/O 2 ratio and temperature play important roles in NO x emission, while the N-gas generation in the oxidation of char is not sensitive to the nascent coal char structure. NO formed in char oxidation tends to be reduced to N 2 at high temperature for a fuel/O 2 ratio of 1.0, which is an optimal condition for NO reduction in decoupling combustion. The reaction pathways revealed for the transformation of N-containing functionalities and generation of NO/N 2 show the vital roles of NH 3 , HCN, char-CNO, and char-NCO in NO x emission. Particularly, the intermediate structures of CNO at coal char provide the very first N to react with NO, leading to N 2 generation. It should be noted that the N 2 in the air would not affect the conclusion regarding fuel-N transfer in the pure oxidation system of O 2 obtained.