Abstract: Based on the mechanism of reducing NOx emission with staged-air combustion technology, the numerical simulation using CFD (FLUEBT6.0) software on the combustion process in the cold and hot states with staged-air technology for a 330 MW coal-fired power plant and the comparison of simulated NOx emission values with the tested NOx emission data were conducted. The results indicate that aerodynamic distribution is symmetrical in a utility boiler with opposed-installation whirl burners. The temperature first rises along with furnace height and then slightly decreases. In the combustion zone, the temperature and NOx concentration are the highest, while the oxygen concentration is the lowest. Without reconstruction and additional equipment cost, the staged-air technology can reach a low NOx emission by regulating some burners for the existing boilers.