The sand mold 3D printer for casting is used to process high-precision sand mold parts. In order to study the influence of the geometric precision of the sand mold 3D printer for casting on the finished product precision of the printed sand mold parts， the topological structure model and the 21-item geometric error model of the sand mold 3D printer can be established through the multi-body system theory. The degrees of fit between different error items and the part printing and processing elements vary， which leads to significant differences in the influencing forces of these error items on different part printing and processing elements. Therefore， the paper proposes a method model for identifying the geometric errors of the typical part printing and processing elements and performing precision compensation on the 3D printer.When considering the processing elements of the sand mold 3D printer， we select the typical parts that the printer can fabricate. For example， spheres， truncated cones， rhombic platforms and rectangular platforms are typical printing and processing elements. Based on the error sensitivity， an analysis of these typical printing and processing elements is carried out， and then the identification of the key geometric errors of the printer is achieved. The identification method model has been experimentally verified on the JCAM-JC1218 sand mold printer. The accumulated influence factors of the key geometric precision sensitivity obtained from the verification are generally greater than 90%. This result indicates that the identification method has high accuracy and reliability under the experimental conditions of real equipment， and can effectively capture the influence factors of the key geometric precision sensitivity， providing strong data support for the further optimization of the performance of the sand mold printer.