A underground room fire was simulated to investigate the effects of smoke exhaust on temperature visibility, soot etc. in the room. A room of $6m{ imes}6m{ imes}2.5m$ with a door of $0.9{ imes}2.0m$ and a 0.5MW polystyrene fire in the room were considered. Temperature, visibility, CO volume fraction and soot were compared for the exhaust velocity at a vent located at the ceiling, 0, 1.2, and 2.4m/s, respectively. Results showed that increasing exhaust velocity decreased room temperature, CO and soot and increased visibility.