Abstract: Through theoretical analysis, the plug-holing is detected as the key factor to influence the efficiency of mechanical smoke extraction of metro station. The simulation software FDS is used to imitate and analyze the average CO concentration in smoke outlet following the changes of the flue gas thickness below the smoke outlet, when the bottom elevations of the hang wall are different under the working conditions of lower smoke vent and lateral smoke vent. The changes of smoke extraction efficiency is comparatively analyzed when the thickness of flue gas below the smoke outlet is different. Finally, the optimal bottom elevation of smoke tube and the bottom elevation of the hang wall in the public areas of metro station are found out.