Abstract: Liquid hydrogen pipeline plays an irreplaceable role in liquid hydrogen transportation, storage, filling and other links, and regular inspection is a necessary means to ensure the safe use of pipelines during pipeline operation. In view of the particularity of the completely closed structure of the inner and outer tubes of the liquid hydrogen pipeline, the liquid hydrogen pipeline can only be tested online. Based on the failure and loss mode analysis of in-service liquid hydrogen pipeline, the on-line detection technology of liquid hydrogen pipeline was sorted out. According to the applicability analysis of the commonly used online detection technology, X-ray digital imaging testing technology (DR) was the best choice for the weld detection of the inner tube of liquid hydrogen pipeline. Through the DR testing of the double-layer tube sample containing the inner tube with defects, the feasibility and effectiveness of the online DR testing technology of liquid hydrogen pipeline were proved.