The steady three-dimensional airflow in subway tunnel was analyzed using ANSYS CFX software and by solving Reynolds-averaged Navier-Stokes equations. A mechanical shaft of existing Seoul subway tunnel was analyzed to apply the developed ventilation system to the subway tunnel. Emergency duct between the ducts of the mechanical shaft was used to connect ducts and install the precipitator. The ducts of the mechanical shaft were connected with two ways such as Duct 1&Duct 2, and Duct 1&Emergency duct. The mass