Abstract: Objective The objective of the present investigation was to determine indoor air quality of No.1 and 2 subway lines in operation in Guangzhou city and the affecting factors Methods Based On the requirements described in"Rules of Health Monitoring for Public Places”，consecutive sampling and monitoring were conducted in all the platforms，lobbies and outdoor environments of the 32 subway sta tions along No.1 and 2 subway lines，and the results were compared Results The concentrations of CO,CO2 and IP in the facilities and environments along No.1 and 2 subway lines in Guangzhou all met the requirements of national standards，with the concentrations of CO and CO2 higher along No 1 line than along No.2 line but the concentration of IP lower along No.1 line Condusion Quality of fresh air，population flow and airflow bear a certain lmpact On the lndoor air quality of the subway stations