Abstract: In order to determine the spatial position of bulk defects in I-shaped weldments, multiple-view method was adopted to test it nondestructively.Mathematic models of small defect depth and deviation for laser weldments with I style were established, and the depth and deviation of small defects in precision weld were determined.Theoretical analysis was preceded on factors, which can influence the locating precision of small defects, and the main influencing factors were obtained.In order to achieve the rapid detection of laser weldments and improve the robust of detection, automatic extraction algorithm of defect projection distance was put forward on the basis of defects segmentation and thinning, and algorithm verification was carried out by using the method of simulation defect.Experimental results show that the extracted method in this paper is feasible.