Abstract: The changes of the air pollutants in Honghe prefecture,as one of the plateau mountainous city in Yunnan province,were analyzed. The backward trajectory model was adopted to explore the main reasons for the key process of pollution. The results showed that in 2018-2020,the atmospheric environmental quality in general has maintained good. The primary pollutantsthat didn't meet the standard are fine particulate and ozone. The air masses from northwestern Vietnam,northeastern Myanmar and northern Laos were relatively poor during the pollution period. The Southern area of Honghe,the northern Vietnam and Laos,and the northwest Myanmar are the potential pollution sources of Honghe.