A heavy-duty natural gas engine meeting China Ⅵ emission standard was taken as the research object. According to the test conditions of WHTC cycle in GB 17691, the effects of exhaust temperature, excess air coefficient and exhaust components on NH₃ and N₂O emissions were investigated at Kunming area. The results show that NH₃ and N₂O mainly generate when the excess air coefficient is small. NH₃ genertes in large quantities at the engine exhaust temperature from 109 ℃ to 326 ℃, while N₂O generates especially at the temperature less than 350 ℃, especially in the cold start stage. The generation of NH₃ and N₂O is greatly affected by the exhaust components of natural gas engine. Under the appropriate exhaust temperature, NH₃ and N₂O emissions increase with the increase of CO, THC and NO emissions. N₂O emission increases and NH₃ emission decreases when SO₂ emission increases. In the WHTC cycle test, NH₃ and N₂O generate in large quantities after 60 s of the start of WHTC cycle test, the generation amount fluctuates greatly in the urban condition and quickly decreases in the suburban condition.