Traveling grate boilers with high pollutant emissions are widely used in China. The main objective of this study is to investigate the characteristics of NO reduction by char layer. Experiments were carried out on a fixed-bed furnace with two different coal bed heights (6 and 12 cm). The concentrations of NO, O-2, CO2, CO, and H-2 were measured and compared to reveal the effect of char layer. Results show that the trend of NO emission presents a double-peak distribution on the coal bed surface for different stoichiometries. The first peak is higher than the second one. The maximum yields of NO emission are 493.30 (6 cm) and 384.09 mg/m(3) (12 cm) for Huainan coal, and 560.19 mg/m(3) (6 cm) and 468.29 mg/m(3) (12 cm) for Mongolia coal. The thicker bed height condition forms more char. The char layer reduces NO generated from the flame front. The presence of CO strongly enhances NO-char reaction.