In this paper, the action of water mist on PVC fires in a cone calorimeter under different external radiant heat fluxes was studied and the reignition of the PVC fires was analyzed. Water mist was generated by a single pressure nozzle. Physical characteristics of the water mist were measured by LDV/APV system. The heat release rate, oxygen, carbon dioxide, and carbon monoxide concentrations and other important parameters of the interaction under various conditions were measured by cone calorimeter. The experiment illustrated that water mist would suppress the PVC fire by evaporation cooling, oxygen displacement and radiant heat attenuation. After the fire was extinguished and water mist was shut off, fire might reignite after a period of time. The reignition time depended on the total quantity of water mist.