Abstract: The vortex and discharge flow with fluctuation of involute type three-lobe positive discharge blowers with countercurrent cooling was numerically investigated by means of computational fluid dynamics(CFD).The dynamic mesh techniques were used to approach the rotating displacement of cell cubage and the alterability of computational area.The non-uniform mesh was applied to the rotor-stator coupled area.The characteristic of inner air flow was discussed.Based on the analysis of instantaneous characteristics of vortex and pulse flow,it's founded that countercurrent cooling could avoid the backflow eddy at the discharge outlet.At the same time,the pulse amplitude in countercurrent cooling is about 20%～25% of that in air cooling in a working cycle.This pulse flow greatly weakened could play an important role in reducing aerodynamic noise in positive discharge blower.