Abstract: To obtain high-accuracy dimensional metrology results of industrial CT, a dimensional metrology method of sub-voxel CT image was proposed for cylinder, which was a common geometric structure in the industry. Firstly, the MarchingCubes method was used to detect the edge points and normal lines. Then the vertices were moved along the normal direction to the maximum gradient. Finally, the point cloud segmentation method was used to get the diameter of the cylinder. The measurement accuracy of this method had been verified in simulation data to be superior to that of the global surface measurement method, and which had a certain engineering application value.