The mass concentration of NO_x in the exhaust gas of the pellet production process of belt roaster is measured to be 135～343 mg/Nm³, and the oxygen content is measured to be 18.23%～19.32%, which is difficult to meet the existing emission standards. By analyzing the source, generation mechanism and distribution of each process section of NO_x and oxygen, the measures and ways to control the mass concentration and oxygen content of NO_x in the exhaust gas are explored and studied. The analysis shows that the main source of NO_x from the belt roaster is thermal NO_x, in which the NO_x production in the roasting section accounts for about 68% of the total production, and the NO_x production in the preheating section accounts for about 32% of the total production, and the measured NO_x mass concentration under the airbox is up to 777 mg/Nm³. The focus of NO_x control should be concentrated in the combustion chamber: the NO_x mass concentration of tail gas can be effectively controlled by using low nitrogen burners, controlling the pellet roasting temperature and the burner gas consumption. The oxygen content in the exhaust gas of the pellet production process can be reduced by adding sealed air boxes in the airbox of the extraction section, installing additional cooling fans for hot air recirculation, and reducing the introduction of cooling air, etc.