Abstract: In this paper, the electron beam welding for the key components of a vehicle engine CR gear weld was taken as the research object, and the ultrasonic C scan detecting and accelerator industrial computed tomography (CT) of the two kinds of nondestructive testing methods were used for contrast test. The results showed that the ultrasonic C scan detecting technology was possessed of high detection rate and high sensitivity for defects such as lack of penetration, partial welding, being not melt and delayed cracks, but the test results were susceptible to the workpiece structures, defect shape and defect size due to ultrasonic probe beam diameter and image boundary segmentation algorithm. On the other hand, the high energy accelerator industrial CT detection systems was better than the ultrasonic C scan in the defect quantitative accuracy for less than 0.5 mm defects and it was not limited by the workpiece structure geometry and shape characteristics of the main defects, and in addition it was characteristic of high resolution and large volume type defect advantage. But the cost of high energy accelerator industrial CT detection device is high, its maintenance is expensive, and its promotion and application is restricted to a certain extent.