Abstract: Ultrasonic phased array technique is adopted to detect inclusion and void which prefabricated in stainless steel weld, and both the testing image and the related A-scan signal characters are analyzed. Scallop scan are used in the experiment, and the testing parameters are adjusted with thickness calibrating course. The results show that ultrasonic phased array technique can be used to measure the defect's location and dimension, which also possess the advantages of more testing range and rich testing information. In conclusion, the image and signal characters which can be use to distinguished inclusion and void are obtained.