Abstract: Aiming at the electron beam welding seam of a certain type of vehicle transmission gear, by comparing the limitations of traditional visual inspection and conventional ultrasonic inspection methods, and combining with the phased array ultrasonic inspection theory, a phased array ultrasonic nondestructive inspection method using a self focusing linear array probe and a short front wedge is proposed, and an automatic phased array ultrasonic inspection system for this kind of gear welding seam is designed. The system can automatically complete all process operations including full record imaging detection of a gear weld, automatic analysis and identification of weld defects, automatic removal and sorting of defective workpieces within 30 seconds, and it has been applied in an automobile parts factory. Combining with the methods including radiographic testing, penetrant testing, and destructive dissection, the secondary verification was carried out. The verification results show that the system is practical and accurate in the welding seam detection of this type of vehicle gear.