Abstract: With the more stringent NO_x emission limit from natural gas fired boiler, the natural gas burner with only one type of low NO_x combustion technologies cannot meet the emission requirement of new-issued standard in Beijing. Thus a new fuel-staged low NO_x burner was developed with the help of the external flue gas recirculation（FGR）, where the NO_xemission goal is below 30 mg/m~3. And an experiment was carried out on the 1.4MWth pilot-scale boiler, and the effects of staged fuel, ratio of flue gas recirculation and excess air on the combustion characteristics and NO_x formation were extensively studied. The results shows that there is an important effect of secondary fuel ratio, excess air and the ratio of flue gas recirculation on the flame stability, and the formation of NO_x. When the ratio of flue gas recirculation increases to 10%, 60% of NO_x emission will be cut down. A fan-shaped stable flame area can be obtained by the effect of ratio of the ratio of FGR and secondary fuel stream.