Abstract: The migration and transformation of N in zigzag char-N with the presence of high concentration NO in the reduction zone is investigated by quantum chemistry method. Transformation characteristics of N in lean oxygen environment are systematically calculated from the molecular level by constructing a char-N model containing a hydroxyl group. The results show that NO in the reduction zone can combine with N in the char to form N₂; and the presence of oxygen enhances the char chemical activity and further promotes the release of N in the char. The co-existence of oxygen and NO in the reduction zone makes the release of N and the combustion of C occur simultaneously, which is manifested by NO and N in the char combining to form N₂, and at the same time oxygen and C in the char formation CO₂ or CO. The kinetic calculations of the rate-limiting step rate constants of the C combustion products show that C is easily oxidized to CO under low temperature and lean oxygen conditions, and with the temperature rise the CO₂ generation rate increases significantly and the high temperature is conducive to CO₂ formation.