Various dies have been used for producing many internal and external parts of an automobile. This paper describes the method of ‘High Speed Die-sinking’ that is one of the key technologies for die-making. We analyzed the milling mechanism of a typical Ball End-Mill used for die-sinking and performed cutting tests. As a result, we have achieved high speed and fine quality die-sinking technology. Its feed speed is about four or five times as fast as before, and the irregularity of the milled surface is under one-fifth as compared with previous level. In addition, we will propose the new method for estimating finishing performance by ball end-mill.