To explore the main reason of air pollution,we analyzed the correlation between monito-ring index of air pollution PM2.5 and other monitoring indexes of AQI,and found that PM2.5 was associ-ated positively with SO2 ,NO2 ,CO,and negatively with O3 and the temperature.Then we got the numeri-cal relationship between PM2.5 and the main factor according to multiple regression model.The results offers...