Abstract: Selecting the air quality data of the high haze season in the Sichuan Basin from 2016 to 2020, the regional pollution types in Sichuan Basin were statistically analyzed. Based on the HYSPLIT backward trajectory model, cluster analysis, potential source contribution factor, concentration weight trajectory and other methods were used to study the correlation mechanism of air quality in the two cities under the condition that Dazhou was polluted earlier than Chengdu. The proportion of type that Dazhou was polluted earlier than Chengdu was highest, accounting for 47%. Under the type that Dazhoun was polluted earlier than Chengdu, the surface wind speed in Dazhou was lower than that in Chengdu, and the occurrence frequency of surface wind speed > 2 m/s (4.1%), which was significantly lower than that in Chengdu (18.7%). The proportion of northeast wind (ENE), northeast wind (NE) and east wind (E) in Dazhou was the highest, which was 16.7%, 16.3% and 15.3%, respectively. Combining the two factors of wind speed and wind direction, the ground of Chengdu was most affected by the northeastward (NNE and NE) air flow, which was consistent with the easterly air flow direction in Dazhou. The results showed that the potential sources of pollution in Chengdu were mainly located in the area from Chengdu City to the southeast of Chengdu, and the rest were in the west of Dazhou, the east of Nanchong, Suining and Ziyang, the junction of Chongqing, the western corner of Chongqing, Zigong and the southwest of Neijiang. Under the weather type that Dazhou is polluted earlier than Chengdu, the impact of Dazhou on Chengdu 's air quality is not the main reason.