Abstract: The efficiency and pressure ratio in a fan stage can be affected,by means of removal of mass flow from the passage.With properly chosen positions and with holes or slots on the suction side of the blades,the fan rotor behaves better in terms of performance.Calculations of a transonic fan rotor,ATS-2,show that the separated-flow area has been observably reduced,and that positive impacts have been observed even with small bleeding mass flow on the rotor.The results also indicate that the bleeding location has a significant impact on the performance.And with adequate air removal,the effect becomes more distinct.