Abstract: Aiming to the testing process of friction stir welding (FSW) for a certain type of aluminum alloy product of carrier rocket tank, nondestructive testing methods such as penetrant testing, phased array ultrasonic testing and radiographic testing were used for comparative experiments. To parts found to have excessive defects, microstructure analysis was conducted through cutting and sampling. The testing results were verified, and finally the types and causes of defects were analyzed. Research results showed that phased array ultrasonic testing had a good effect on testing incomplete penetration defects and kissing bonding defects at the root of aluminum alloy friction stir welding. It can accurately locate defects, measure the depth and length of defects, and complement the deficiencies of other nondestructive testing methods, it provides a reliable means for nondestructive testing of similar structural products.