Abstract: Ultrasonic TOFD (time of flight diffraction) B-scan cannot be carried out because of the weld reinforcements. Aims at the problem, transverse position measurement methods for weld defects are proposed, including double ellipse based method and longitudinal-shear wave composite method. According to the geometric relationship between probe and defect position, two mathematical models of defect localization are established. Using the algorithm, the position of the artificial defects and actual defects are measured. The analysis and comparison results show that the double ellipse method is better than the longitudinal-shear wave composite method in terms of accuracy and implementation. Using double ellipse based method, the average errors of buried depth and transverse position of artificial defects are 0.5 and 0.3 mm respectively, and the average errors of buried depth and horizontal position of weld defects are 0.6 and 0.4 mm respectively. The proposed method effectively overcomes the disadvantage of limited accessibility of traditional ultrasonic TOFD B-scan because of the weld reinforcements, and provides a solution for the detection of the transverse position of the defect in the weld.