Abstract: The nickel-base welding seam of dissimilar steel is easy to break during operation because of high temperature fatigue, and in order to avoid this kind of accident, a method of using phased array ultrasound to detect the welding seam of nickel-based dissimilar steel is presented in this paper. The structure, metallographic structure and acoustic characteristics of the weld are analyzed. The difficulties of ultrasonic detection of this kind of welds are clarified. Combined with the characteristics of phased array ultrasonic detection, the above difficulties are overcome by controlling the technical parameters of the detection. The feasibility of phased array ultrasonic detection of this kind of weld is analyzed theoretically.