This paper deals with an experimental study on the influence of coal quality on nitrogen oxide (NOx) formation and unburned carbon in fly ash. Three Chinese coals (lean coals and bituminous coal) have been fired in three tangentially full scale boilers (about 300 MWe power units, 1000 t/h boilers) and in two pilot scale test furnaces (the drop-tube furnace (DTF) and the single burner furnace (SBF)). In furnace NOx emission and unburned carbon in fly ash have been measured synchronously with different combustion condition. Identical trends in NOx emission as a function of coal analysis content and excessive oxygen content have been obtained. NOx emission was found to correlate well with the fuel nitrogen content of the coals. Coal quality characteristic, especially ash content, and operation condition have been studied on the influence of furnace burnout performance.