Abstract: FDS ( fire dynamics simulator), a field simulation software, was used to investigate the spread regularity of smoke and its influencing factors in order to determine the reasonable relative position of smoke tower and passageway ofa subway station to prevent the smoke extracted through the smoke towerwhen a subway fire occurs running back into the station. The simulation results indicates that the possibility that the smoke extracted through a smoke tower runs back into a subway station through its passageway is related to smoke temperature, spatial distance between a smoke tower and a passageway, and direction and strength of nature wind and so on. A field experiment shows the availability of the simulation results.