Abstract: Taking the digital detector array (DDA) detection technology as the research object, length of one transillumination of longitudinal seam transillumination, girth weld center transillumination, girth weld source external double-wall single shadow transillumination, girth weld source inside single wall single shadow transillumination in digital X-ray inspection of pressure pipeline were deduced and calculated, which provided a theoretical basis for the DDA detection of pressure pipeline welds.