Abstract: Objective To investigate the sanitary status of air in the metro, analyze the impact of passenger volume and environmental air quality on the air quality in the metro, and provide scientific evidence for the prevention of diseases. Method Air quality in the station hall, platform, train carriages and the entrance of fresh air of a representative metro line was monitored continuously according to the Technical Rules of Health Monitoring for Public Places (GB 17220-1998). Results Majority of monitoring indicators were under the relevant health standard limits, but the temperature, relative humidity, wind speed, noise, carbon dioxide and nitrogen dioxide were still exceeded the standard limits. The relative humidity, carbon monoxide, carbon dioxide and total bacteria counts monitored during passenger flow peak periods and off-peak periods were statistically different (P < 0.05). The inhalable particulates, nitrogen dioxide, sulfur dioxide and ozone in the station hall and fresh air entrance were not statistically different (P＞0.05), but they were significantly correlated (P < 0.05). Conclusions Passenger volume and environmental air quality were two important factors that could affect air quality in the metro. Air quality was relatively poor during peak passenger volume time. Environmental pollutants could pollute the air in the metro through fresh air entrances. Strengthening the design of metro-related health facilities and good sanitary administration would be helpful for the guarantee of indoor air quality in the metro.