In this study, the crankshaft pin grinding mechanism, which is carried out with wheel head oscillating type CNC crankshaft pin grinder, is theoretically analyzed. In order to maintain grinding process, the pin rotates and also rocks along wheel working surface, because the wheel head oscillates with journal rotation. Then, it is made clear that cylindrical plunge grinding process progresses in the pin grinding process for the first time. Therefore, grinding speed ratio, which is defined as ratio of substantial pin surface speed to wheel surface speed, is firstly formulated. Secondly, undeformed chip size generated by a grain is estimated with the grinding velocity ratio. Finally, the grinding performance is predicted with experimental equations, which obtained previous study. By this simulation, it is made clear that dimensional accuracy and also surface roughness vary on whole of the pin surface with constant journal rotation grinding method. On the contrary, deviations of both the dimensional accuracy and the surface roughness are reduced with controlled speed ratio grinding method, in which journal rotation speed is adequately controlled.