Abstract: In view of the complex acoustic characteristics and defect display of deep defects in welded joints of key parts such as welded structural parts of rail train bogies, the phased array detection results of different shapes and sizes of defects were analyzed, and the influence of sound field mechanism of mild steel deep defects on phased array detection results were expounded in combination with sound field propagation simulation results. At the same time, the 3 D visualization of different defects was realized based on OpenGL. The results showed that the strip defect had stronger reflection effect on the vertical direction of the phased array sound field, and the acoustic shadow area increased with the decrease of the defect width. Meanwhile, the phased array sound field with more concentrated reflection at the defect had higher detection sensitivity and resolution. The defect 3 D display results based on 3 D database could clearly and intuitively reflect the internal defects of components. This research had practical significance for ultrasonic phased array detection and three-dimensional visualization of defects in welded structural parts of high-speed train bogies.