Taking a certain type of CNC crankshaft grinder as the research object, the structure and motion of the grinder were analyzed, and the ideal wheel trajectory equation for crankshaft grinding was derived. According to the multibody system theory, a model containing error parameters was established, the kinematic chain position matrix of the machineworkpiece and the machinetool were established, and the constraint equations of the precision machining of the machine were obtained. The geometric error of the grinding machine was studied, and a geometric error model was established. In order to quickly and accurately identify various geometric errors, a hybrid SAPSO-GA algorithm was proposed. The compensation effect was analyzed by comparing the motion trajectory before and after compensation with a ballbar. The results show that the identifying accuracy of the method is improved, and the machining accuracy of the crankshaft grinder is greatly improved through compensation.