Abstract: To solve the rather low recognition capability of near surface defect in ultrasonic time of flight diffraction method, a near-surface defect detection method based on the through wave amplitude distribution analysis is proposed. Several key points in the part of through wave of testing signal are extracted and relationship between the amplitude distribution of key points and depth of near-surface defect is analyzed. The characteristic numbers of amplitude distribution which can be used to test near-surface defect is obtained. The experimental results showed that this technique could accurately detect the artificial defects with buried depth of 1.0mm, and the recognition ability to near-surface defect was effectively improved.