Abstract: A tunnel model(6m×15m×2m) was designed to do the firesuppression experiment under the joint action of top smoke discharging and water mist. The temperature of the smoke and flame， the concentration of CO， as well as the visibility of smoke were measured to analyze the suppression and cooling effect on fire and smoke under different coupling modes of water mist and top smoke discharging. The results show that top smoke discharging accelerates the burning rate of diesel oil， and cooling effect is obvious under the coupling mode. In the fire growth stage (50s)， water mist coupled with top smoke discharging has the optimal control effect on smoke. Whereas it is easy to lead boil over and flashover in the fire fullydeveloped stage (90s). Meanwhile， the flame enhancement is most obvious and the concentration of CO increases sharply. Top smoke discharging can greatly improve the visibility， and water mist alone can control the smoke effectively but decrease the visibility. The increasing rate of visibility can be accelerated because of the sedimentation of smoke absorbed by water mist combined with top smoke discharging.

Key words: top smoke discharging, visibility, fire, water mist, firesuppression experiment