Subway becomes more and more main transportation in major cities. Air pollution in the subway platforms is decreased; however, dust flow inside subway tunnel and train is increased by installing Platform Screen Door. Airflow inside subway tunnel is observed using computational method in this study. The airflow characteristics around ventilation shafts and inside the tunnel is studied following the train movement, while the train moves from existing Miasamgeori station to Gireum station. ANSYS CFX V12.0.1 and ICFM CFD V12.0.1 are used to compute the airflow inside the subway tunnel.