Abstract: The 3D imaging method based on volume rendering algorithm was used to reconstruct the original phased array ultrasonic testing data. At the same time, in the three-dimensional model, the relevant display signals were identified based on clustering algorithm, measured and evaluated according to the standard requirements. The butt weld test block was designed and tested by using the test block data. The result showed that the designed automatic analysis system can directly display the imaging effect, had fast response speed, high recognition and measurement accuracy. The efficiency of automatic analysis was more than 3 times higher than that of manual analysis.