Abstract: A segmented synthetic C-scan imaging method for phased array ultrasonic testing was introduced. Firstly, the limitations of traditional imaging methods were explained through the problem of ineffective detection of defects encountered in phased array ultrasonic water cooling detection. The birth reason of the segmented synthesis C-scan imaging method was introduced, and then the specific principle and implementation method of this method were introduced. Finally, by comparing the imaging results before and after the application of this method, the advantages and application scenarios of this method were summarized. Compared to traditional phased array ultrasound and ultrasound microscopy imaging, the partitioned synthesis C-scan imaging method can be better applied to the detection of various complex multi-layer structure workpieces, including water-cooled plates.