Abstract: A method of ultrasonic vibration + cryogenic liquid nitrogen + frozen support layer (UCF) is proposed to assist carbon fiber reinforced polymer (CFRP) drilling and effectively reduce machining defects. The basic principle of this method is as follows: the high frequency vibration of the drill bit under ultrasonic action is used to weaken the axial drilling force; the cryogenic temperature liquid nitrogen and the formation of frozen support layer are used to realize the constraint and support of the material at the drilling exit side, and effectively reduce the whole process of drilling heat effect. Based on the basic principle of UCF, corresponding experiment of UCF assisted drilling were carried out, and the hole quality of CFRP under traditional drilling mode (TD) and cryogenic liquid nitrogen + freezing support mode (CF) was compared and analyzed by means of microscopic inspection and characterization and defect factor calculation. The results show that both UCF and CF can increase the axial force, but the maximum axial force increased little. Compared with TD mode, UCF can reduce burr factor by 75%, tear factor by 8.9%, delamination factor by 34.6% and surface roughness R_a by 53.6%.