Abstract: Based on the characteristics of digital image in digital radiographic testing technology and the influence of window width and window level adjustment on the display effect of digital image, the idea that the resolution of defect vision should be verified at the thinnest part before the formal inspection to solidify the window width and window level was proposed when the workpiece with variable cross-section is tested, and the circumferential weld of thin-walled small diameter aluminum alloy pipe should be tested to verify the effectiveness of this idea. At the same time, the influence of the tooling plate of the fixed gasket on the inspection of the thin-walled tube was discussed, which was approved by the special process review.