Abstract: The high resolution industrial CT image is useful for its three-dimensional information of the object. In the testing of the defect of workpiece, the testing efficiency by using image segmentation method to recognize and reveal the defect is enhanced. The bit-window method in the preprocess of the CT image and two-dimensional histogram method in the image segmentation were successively adopted and the defect of a inspected workpiece was revealed very well. Further more, these methods can solve similar problems.