Domestic and international research has shown that the air quality in the subway is not optimistic. The concentration of major pollutants such as fine particulate matter (PM2.5) in the subway is significantly higher than the outdoor level. The ambient air quality in the subway affects passengers and subway workers. Health effects that cannot be ignored. Under the background of the improvement of outdoor ambient air quality throughout the country, the air quality in densely populated and relatively closed subways has gradually become a topic of concern for policy makers and the public, but there are still no corresponding regulations and policies to deal with this challenge. This project hopes to compare domestic and international standards on subway air quality and share best international practices and promote domestic discussions and establish subway air quality standards.