It is difficult to analyze the shape and position error of internal surface of parts with complex cavity structure. To address this issue, a method of analyzing the shape and position error of complex cavity of parts is proposed, which is based on industrial CT technology. First, the parts are scanned by using industrial CT and reconstructed into the measurement STL model. Then, the design IGES model is discretized into the STL model and the measurement STL model for registration. Secondly, by using the designed IGES model as the guide, the points in the STL model and the belonging of each surface of the IGES model are determined. And all the surfaces in the STL model are automatically segmented and measured. Finally, the surface of IGES model is selected and the point cloud cluster corresponding to the surface is analyzed. The valve body model of the million-dollar measurement point cloud is selected for the experiment. All the surfaces of the point cloud model are completely segmented. The cylindricity, flatness and parallelism of the selected internal surface are measured to be 1. 11 mm, 0. 61 mm, and 1. 92 mm, respectively. In this method, only the input STL model of part measurement and the IGES model of part design are required. The measured surface of IGES model is selected. The internal and external surface of part can be analyzed automatically.