Abstract: According to the principles and physical characteristics of ultrasound, a new idea is put forward making use of ultrasonic to detect weld imperfection in shipbuilding. On the basis of the rate of acoustic impedance, an iterative reconstruction algorithm is used to rebuild the 2D image of weld defect. Considers ultrasonic echo as the point locus of the point that the distance between the launching point and defect point is equal to the distance between the defect point and the receiving point, and then has the line integral of the change rate of acoustic impedance. The method improves the resolution of ultrasonic imaging effectively.

Key words: acoustic impedance, image reconstruction, ship weld