Abstract: At present, there are some shortcomings in NDT of aluminum alloy shell used for high-voltage switch-gear. Based on the advantages of phased array testing, exploring whether the gear is needed to be replaced is the aim of current research. In the paper, the butt welding commonly used in the aluminum alloy with base material thickness of 10 and 16 mm respectively is used. The self-focusing probe and conventional probe were used for comparative analysis aiming to evaluate test accuracy. The test results show that for 10 mm aluminum alloy welded joints, the self-focusing probe can detect all prefabricated defects and obtain more defect characteristics information. For 16 mm aluminum alloy welded joints, affected by the focusing area, the conventional probe can detect all the prefabricated defects, and the defect detection rate and defect quantitative accuracy are higher than that of the self-focusing probe.