In order to find a suitable error separation method,taking the CNC crankshaft oscillating grinder as the object,the factors effecting the crankshaft pin journal contour error were divided into the following factors and the unfollowing factors.The basic principle of the crankshaft oscillating grinding and the accurate modeling method of the crankshaft pin journal contour generation were described.The method of separating the contour error into the following error and the unfollowing error was proposed.Through the experimental data analysis,the performance evaluation conclusion about the CNC crankshaft oscillating grinder was obtained.The proposed separation method of contour error can provide methodological guidance for the performance evaluation of CNC oscillating grinder and the judgement basis for the error source identification.