A new diamond tool for machining cemented carbide counterbore and its processing technology are introduced. The relationship between the machining efficiency and the service life of the diamond grinding head is studied under the conditions of different cutting depth and feed speed by using the electroplating and sintered diamond grinding head on NC milling machine. The effects of different size and groove electroplating and sintered diamond grinding head on the efficiency and the precision of the cemented carbide counterbore with different materials are studied. The micro-structure of the diamond grinding head is analyzed by SEM and optical microscope. Results show that the sintered diamond grinding head has better working life and efficiency. The processing time of the per counterbore (φ13 mm×5 mm) of the traditional cemented carbide is shortened from 2 hours to 10-15 min, and the serving life of each sintered diamond grinding head can reach 33-40. The application of hard and brittle materials with counterbore machining will be promisingly expanded.