Abstract: In order to accurately locate and identify the location of near-surface defects in low-alloy plate butt weld, the D-scan image obtained by the time of flight diffraction method was processed. In order to accurately locate the depth of defects, a through wave straightening technology based on the peak detection algorithm-PDA was proposed; in order to recognize near-surface defects, then a through wave cancellation technology based on A-scan line energy distribution algorithm-EDA was introduced. The experiment results showed that the proposed method effectively improved the recognition ability of near-surface defects. By this technology, the depth of defect could be located more accurately and the near-surface defects could be recognized more clearly, and hence accurate location and recognition of defect was achieved.