In this study, the grinding mechanism of the crankshaft pin carried out by the CNC crankshaft pin grinder, is theoretically analyzed. By this grinder in the grinding process, the geometrical interference form varies continuously, because the substantial grinding speed at the grinding point changes due to the revolution of the pin. Therefore, the grinding mechanism in the CNC camshaft pin grinder is made clear, from the investigation of the various relation of the speed at the grinding point. Furthermore, the control methods of the constant grinding velocity ratio and of the constant residual stock are proposed in order to regulate the variations of the grinding results. In these methods, the journal rotation angle velocity is controlled to maintain the size of the geometrical chip shape constant, and the high performance pin grinding ability is verified.