Abstract: Through detailed technical analysis on an explosion accident in a long-distance gas pipeline, the cause of its explosion and leakage and the ignition source were found out. Visual inspection and measurement were carried out on the fracture of the explosion pipeline, and macro-morphology of fracture was analyzed. Samples were taken from both the exploded and unexploded pipes to conduct chemical composition analysis and metallographic analysis. Massive samples were taken transversally along the explosion pipeline to conduct tensile property test. Microhardness test was carried out on the cross section of the exploded and unexploded pipes. Samples were taken respectively from the exploded pipeline near the scratch area and the unexploded one to test the hydrogen content in the metal. Fracture was observed under the scanning electron microscope. Based on all the above studies, the cause of pipeline fracture was determined, that is, the serious scratch on the surface of pipeline causes the hydrogen induced cracking of pipeline, which then led to the leakage of natural gas, then natural gas mixing with air formed the explosive gas mixture, which when meeting the discharge spark of insulator in power supply line, exploded. In the end, effective preventive measures are proposed in terms of integrity management, inspection of external anticorrosive coating and cathodic protection.