In this article, the results of an optimization study when internal grinding C45 carbon steel were introduced. In the problem, the objective function which was chosen is the minimum machining time. Besides, six main process parameters including the initial grinding wheel diameter, the grinding wheel width, the wheel life, the total depth of dressing cut, the radial grinding wheel wear per dress, and the tolerance grade were selected for the problem. The influence of these parameters on the optimal replaced wheel diameter was analyzed by designing and performing a simulation experiment. In addition, a regression formula to calculate the optimal replaced wheel diameter was found. It was reported that this formula is in good agreement with the experimental data.