Abstract: The variation in the oxygen content at the fan mill outlet will directly affect the combustion efficiency of lignite and the formation of nitrogen oxides( NO_x ).In this paper,Fluent 15.0 software was used to calculate the flow,combustion and NO_x formation characteristics of the fuel in the tower furnace under the condition of 8%,10%,12%,14% and 16% of the oxygen output at the fan mill outlet of a 660 MW supercritical unit.The results show that the fuel gas temperature at the flame center and the furnace outlet decreases significantly with the increase of the oxygen content at the outlet of the fan mill.Adjusting the oxygen content at the outlet of the fan mill can effectively control the central position of the flame and the fuel gas temperature at the hearth,avoiding excessive temperature of the flue gas and causing coking at the smoke outlet.Meanwhile,the NO_x content at the outlet of the furnace increases with the increase of the oxygen content at the outlet of the fan mill.After comparing the combustion characteristics of the pulverized coal and the NO_x generation rules under different oxygen conditions at the fan mill outlet,it is concluded that the optimum oxygen content at the fan mill outlet is 10%.