Abstract: The effect of air intake and exhaust on the aerodynamic performance of flying wing UAV is investigated in details. Model description and experimental setup is introduced, experimental results are analysized. The longitudinal aerodynamic performance variations among different flow flux, the aerodynamic performance variations among different eject pressure ratio, the lateral and directional aerodynamic characteristics of UAV and the comparison of the aerodynamic performances of the flap with and without eject are presented. The air intake and exhaust can increase the value of drag and the value of pitching moment, the liftdrag ratio will decrease 1 to 4,but the eject has little effect on the pitching moment. The Sshaped inlet has important effect on the pitching moment, the liftdrag ratio will decrease 11.8 by eject. Finally, Air intake and exhaust have little effect on the lateral and directional aerodynamic characteristics of UAV and flap efficiency.