To solve the delamination defect that was easy to occur in the traditional drilling process of carbon fiber reinforced plastics (CFRP), the analyses of delamination and suppression mechanism during ultrasonic vibration core drilling (UVCD) of CFRP were implemented based on the diamond core drill and ultrasonic vibration machining technology. The delamination mechanism and evaluation in traditional drilling of twist drill and common core drilling (CCD) of diamond core drill were analyzed by theoretical method, the delamination suppression mechanism of UVCD was also analyzed, which was verified by experimental method. The results show that compared with the CCD of CFRP, the UVCD can effectively improve the cutting performance and chip removal effects of diamond core drill, reduce the thrust force by 12.5%~19.2%, suppress the chip adhesion and rod jamming of diamond core drill, suppress the formation of delamination defect of CFRP as well as improve the surface quality of machined hole.