Abstract: It is extensively applied in NDT (Non-destructive testing) of fusion welding seam. Firstly, the status of this technology in defect inspection of fusion welding seam was expounded in three aspects: innovations of conventional ultrasonic testing, new techniques of ultrasonic testing, and ultrasonic signal processing. Secondly, theories, methods and application situation of fusion welding residual stress measurement by ultrasonic testing were introduced. Finally, this paper summarized limitations of ultrasonic testing and prospected the future trend.