Abstract: Ultrasonic testing of hydrogen pipeline in service does not belong to the standard requirements. According to failure cases, the ultrasonic testing has been increased. The test method of longitudinal defect and parameters of ultrasonic testing have been introduced, the defect causes have been analyzed. The production method of the two kinds test block, the grinding method of the probe, the using method of the probe, the harm of grinding probe errors have been to highlight. After ultrasonic testing, superscalar signals of pipeline have been discovered and the hydrogen pipeline has been replaced. So far, the pipeline has been running for two years, no abnormal condition were found.