Abstract: Diamond core drill bit for sapphire is different from the conventional engineering drill bit, it requires good sharpness, long life, small radial jumping, good surface quality of sapphire bar, so the higher requirement is proposed for the preparation and testing of drill bit.This paper focuses on the important testing indicators of the segment, the drill pipe, the matrix design and the finished drill bit, and elaborates the key details on the preparation of segment, the welding of bit and the subsequent processing.We prepared a 4-inch (internal diameter ϕ103 mm) diamond drill bit for drilling sapphire crystal, the efficiency is increased by 12% than the Taiwanese company's drill bit with the same specifications, the life is about 95% of Taiwanese company's drill bit, and the defective rate of sapphire bar is less than 0.5%, which satisfies the requirement of customers.