Abstract: In order to evaluate the effect of defects on the weldment, analysis welding process and repair the weldment, it is necessary to get the buried depth of weld internal defects accurately. This paper introduces the principle of two kinds of defect location methods based on X-ray technique, including double labels translation and rotation methods. The accuracy of the two methods is verified through testing the buried depth of artificial defects and weld defects. The experimental results show that the double labels translation method, which based on the parallel beam assumption, lacks in accuracy compared with the rotation method. For the wledment 8 mm in thickness, using the double labels translation method, the maximum absolute error of defect depth obtained is 1.9 mm, and the average absolute error is 1.4 mm, and the average relative error is 18%. Using the rotation method, the maximum error is 0.5mm, and the average error is 0.3 mm, and the average relative error is 4%.