Abstract:With social and economic developmentꎬpeople increasingly pay attention to air quality.In this paper we classify the air quality of 31 provincial capitals and municipalities according to the detectable air quality indexes through cluster a ̄ nalysis.At the same timeꎬ we use factor analysis to integrate the indexes of the factors affecting air quality into minority key indexesꎬ and also designate the factors. With these we can comprehensively work out the major factors affecting the air quality.