Abstract: In order to improve the detection and identification of underexposed small-diameter pipe girth weld defects, digital radiography (DR) was used to complete the safety monitoring of pressure vessels in nuclear power plants. Guided filtering and dark channel demisting theory were combined to enhance the DR Image of small-diameter pipe girth weld at low dose. The image quality was evaluated through objective evaluation indicators, and compared with adaptive histogram equalization (AHE) and contrast limited adaptive histogram equalization (CLAHE) image enhancement methods. The results show that the dark channel image enhancement technology has a better impact on image quality improvement, the image contrast-to-noise ratio was increased by 31. 5% and signal-to-noise ratio was increased by about 1. 5 times, and the defect contour was clearer.