Abstract: In this paper, two groups of different types of defective specimens were designed and manufactured through high-precision metal additive manufacturing technology. Based on the micro-CT detection technology and the defect anatomical metallographic detection method, the actual detection ability of micro-CT on small defects of additive manufacturing was studied. The research results showed that micro-CT can effectively detect the artificial defects of 20 μm under the voxel size of 5 μm; metallographic detection and CT detection results were basically the same, and the difference in the measurement of the defect size was less than 10 μm; the defects of smaller sizes were more inaccurate due to the influence of the partial volume effect of the dimensional measurement results.