Abstract: Some power plant pipelines are welded by nickel-based welding rods. When using conventional ultrasonic testing technology to detect such welds, the coarseness and anisotropy of the weld grain structure have a great influence on the quantitative and localized analysis of ultrasonic testing. Therefore, there is a lack of effective means for monitoring the quality of the inside of the nickel-based weld. The advantages of phased array ultrasonic testing technology are analyzed. A dual array low frequency longitudinal wave detecting method for phased array ultrasonic testing of nickel-based welded joints is proposed. The test is verified by the combination test. The results show that the signal-to-noise ratio of the detection process meets the relevant standards of process requirements. The defect positioning deviation is analyzed, and the correction method is proposed. The corrected defect positioning accuracy is over 90%.