To investigate the effects of fuel NO formation models on the prediction of NO concentrations in a coal combustion field, numerical simulations for a coal combustion field in a 760 kW test furnace were performed. Three models, those proposed by De Soete, Chen et al. and Mitchell et al. were employed to calculate fuel NO formation originating from volatile matter. The results show that the model proposed by Mitchell et al. reproduces the tendency of the experimental data better than the other two models. In addition, the difference between the NO conversion ratios of bituminous coal and sub-bituminous coal that contains a high level of moisture was examined in detail using simulation results from the model of Mitchell et al. It was found that the formation of a region with a low oxygen mole fraction immediately downstream of a region with a high NO production rate is essential to realize a low NO conversion ratio. (C) 2016 Elsevier Ltd. All rights reserved.