Abstract: Aiming at the difficult problem of the TOFD(time of flight diffraction)method testing the internal defect types of the steel structure bridge butt welds, 12 artificial simulation specimens containing typical weld defects were designed and produced, and TOFD testing was carried out, and the weld defects TOFD-D were compared and analyzed. Scan image features. The test results show that different types of defects have obvious TOFD-D scan image feature differences. By analyzing the texture, shape and direction of the D scan image, the typical defect types of butt welds can be determined based on the TOFD-D scan image features.