Abstract: The sand molding machine is used for processing complex sand mold parts. The geometric error of the molding machine has 21 items, and each error item has a significant impact on different elements of the part processing. Therefore, this article proposes to identify the key geometric errors and related compensations for typical part processing elements, and to improve the accuracy of sand mold parts processing through compensation. Taking the typical processing elements of sand mold parts processed by the sand molding machine as an example, firstly, the typical processing elements include four typical elements: cylindrical platform, conical platform, diamond platform, and inclined quadrangular platform. Secondly, based on the sensitivity analysis of errors, the key geometric errors corresponding to the typical processing elements are identified. Finally, targeted compensation is carried out according to the typical part processing elements. The experimental verification is conducted on the CAMTC-SMM2000 sand molding machine, and the sum of the sensitivity influence factors of the identified key geometric errors is all greater than 90%. After implementing error compensation, the processing accuracy of the four typical part processing elements is improved by 55%～70%. The results show that this method can effectively identify the key geometric errors under different part processing elements and improve the processing accuracy of sand mold parts.