The formation mechanism of nitrogen oxides and the reduction of O2/CO2 combustion and air combustion were studied. The ratio of O2/CH4 in primary schools has reached the lowest fixed nitrogen compound for O2/CO2 combustion, which is lower than that for air combustion. The lowest conversion rate of nitrogen oxides is 40% lower than that of O2/CO2 combustion in air. This can be explained by high carbon dioxide concentration, which is one of the most important characteristics of O2/CO2 combustion. The results show that O2/CO2 combustion forms a large number of OH radicals through CO2+. →CO+OH***, regardless of experiment and numerical simulation. H+H2O and O2+ produced by OH radical→ H2+? → hydroxyl hydrogen, oxygen free radical? The source of a lot of hydrogen is methane in the flame. The formation of O and OH radicals in the fuel-rich region promotes the oxidation of NH3 and HCN. In staged combustion, NH3 and HCN are actively converted into NO, and the main fuel-rich areas have high reduction activity, because these intermediate nitrogen species can easily convert secondary oxygen intoNO. Finally, when the emission of nitrogen oxides is greatly reduced, it is possible to switch to O2/CO2 combustion with low O2/CH4.