Abstract: Manual ultrasonic testing system of weld defects based on video positioning of USB camera was studied. The planar position of ultrasonic probe relative to the weld bead was obtained by USB camera, and the depth of weld defects was obtained by ultrasonic probe. Then the locational qualitative and quantitative analysis on weld defects was obtained by the method of three-view projection imaging technology intuitively. This system is applicable to the field test of welded structure on service. Ultrasonic testing was performed to the actual weld, including crack defect by this system. The result showed that the location, size and distribution of weld defects could be characterized conveniently, quickly and intuitively, and the method was helpful for the qualitative recognition of different weld defects.