Air quality is related to people's health, and in today's rapid development of industry, the research of air quality is more and more important. The author selected two pollutants that can represent air quality, sulfur dioxide and particulate matter 10, and used the R/S analysis method in the time series to study the monthly data of these two pollutants in Xi City from August 2018 to August 2022, and found that the regular changes of these two pollutant indices on the time scale, that is, the natural year is generally used as a cycle. The previous pollutant index has a continuous impact on the future pollutant index. Finally, based on the unique geographical location of Xi in the Guanzhong Plain, the possible reasons for the change in pollutant index were speculated. It is hoped that this article will be helpful for the prevention and control of air quality in Xi'an in the future.