Based on the original data of air quality in 31 major cities in China, the average monthly concentration of fine particulate matter, inhalable particulate matter, sulfur dioxide, carbon monoxide, nitrogen dioxide, ozone and the days with good quality grade were obtained. Based on these data, cluster analysis and principal component analysis were done. The conclusion is that the air quality of Fuzhou, Haikou, Guiyang, Kunming and Lhasa is high,and in Shijiazhuang, Taiyuan, Jinan, Zhengzhou and Xi'an is low.The negative effect of ozone and sulfur dioxide in the main component is large, and the overall main component result has the greatest effect of nitrogen dioxide on air quality. Corresponding suggestions are proposed based on the results of the research analysis.