This study reports an experimental investigation on the nitrogen oxide (NOx) emissions in pulverized fuel (coal and char) combustion through preheating with a circulating fluidized bed. The high-temperature preheated fuel particles obtained from the circulating fluidized bed would be burned in the down-fired combustor. The focus of this research is the trend of NOx emissions with different air distribution through varying secondary air nozzle structures and air ratios as well as tertiary air positions along the down-fired combustor. Under stable operation, the burning temperature was uniform and the combustion efficiency was high. When the fuel was pulverized coal, the NOx emissions with the secondary air center nozzle structure were almost twice of that with ring nozzle Structure. Furthermore, the NOx emissions increased with an increase of secondary air ratio when the nozzle structure was in the center. However, there was a minimum NOx concentration when the nozzle structure was a ring. And, the lower NOx emissions were achieved through arranging the tertiary air distribution rationally. In addition, the trend in NOx concentration along the down-fired combustor was almost the same irrespective of the fuel (coal or char). But, the char combustion efficiency should be paid more attention when the tertiary air position changes.