Abstract: The automated extraction algorithm of spatial position data was provided for small defects in double T style weldments.It consists of two parts,one is that automatically extracts projection distance and the distribution of defects along the weld longitudinal direction,and the other is that automatically extracts defect dimension and the distribution of defects along the weld longitudinal direction.Automated corresponding criterion is designed for the defects of left and right turning images in double T joints,and quick extraction of spatial position data for small defects is achieved.Then algorithm verification is carried out by using destructive test of real weldments.The results show that the provided algorithm is feasible in this paper.