Abstract: Ammonia(NH₃) is a type of carbon-free and hydrogen-rich fuel, which can achieve zero-carbon emission during combustion. However, the N contained in ammonia may be oxidized to form nitrogen oxide pollutants(NO_x), causing atmospheric environmental pollution. Therefore, based on quantum chemical calculation, the evolution process of H₂NO intermediate during ammonia combustion is studied at the microscopic level, and the impact on NO_x generation is analyzed. The theoretical calculation results indicate that the H₂NO is an important intermediate for the generation of NO, which is generated through the decomposition elementary reaction of nitrogen oxides with an activation energy of 93.53 kJ/mol. The dehydrogenation product of H₂NO, HNO, is a key intermediate for the generation of NO₂, which is generated through the oxidation elementary reaction of nitrogen oxides with an activation energy of 43.73 kJ/mol. From the perspective of quantum chemistry, high temperature conditions increase the activation energy and the Gibbs free energy of the NO and NO₂ generation reaction, while high pressure conditions barely have effect on it during the ammonia combustion process. This study can provide theoretical reference for reducing NO_x generation during ammonia combustion.