Abstract In order to further investigate the second rise phenomenon of NO in pulverized coal boilers, the simulated air-staged combustion atmosphere was used in a high temperature fixed bed reactor to study the heterogeneous reduction mechanism of N2O and NO formation. The results show that proper conditions can converse N2O to a large amount of NO. The reduction ability of char to NO produced by N2O in different atmospheres is not much different, but it will be greatly reduced at high temperature, indicating that the ability of char to prevent the second rise of NO is limited. In the oxidizing atmosphere, three reaction paths of N2O heterogeneous reduction were verified through the reduction of N2O by char under different oxygen concentrations. Low O2 concentration at low temperature improves the char’s reducing capacity, while at high temperature it enhances the oxidation capacity of O2, promoting the oxidation consumption of char. The coexistence of iodine and char will reduce the effect of iodine on inhibiting the formation of NO, as well as char’s reducing capacity. The iodine can promote the decomposition of N2O and inhibit the adsorption of N and O on the char surface.