Residence time is a key parameter for the cyclones with mass transfer or reaction process. A model for the cylinder-on-cone cyclone was presented to calculate the mean residence time of the liquid phase, based on a force balance on the wall film. This model was validated using an experiment, which measured the residence time of the liquid phase by the hold-up method. The results demonstrated that the predicted residence times are in good overall agreement with the measured values. Furthermore, the liquid residence time decreases obviously with increasing droplets loading, and decreases less with increasing inlet velocity. The liquid residence time increases with the cylinder diameter. The wall film velocity, however, decreases with increasing cylinder diameter, because the perimeter of liquid wall film is directly proportional to the cylinder diameter.