Abstract: In order to find out the cause of leakage of a buried process pipeline in a natural gas transmission station, the leaked pipe section intercepted on site was detected and analyzed by means of macro-morphology analysis, geometric dimension detection, nondestructive testing, physical and chemical performance test, scanning electron microscope and energy spectrum analysis, and X-ray diffraction analysis. The results show that, the two leakage points in the girth weld of the leaked pipe section are caused by the connection of the corrosion pits on the outer surface and incomplete penetrations of the weld root with each other in the fusion area. The main leakage reasons of the two points in the girth weld are oxygen absorption corrosion on the outer surface and incomplete penetration defect at the root. The leakage point at the outer arc side of elbow is caused by the corrosion perforation when the anti-corrosion coating falls off, the oxygen absorption corrosion on the outer wall is the main reason for its leakage. It is recommended to regularly carry out the hidden danger investigation of girth welds and anti-corrosion coatings for old buried pipelines in natural gas transmission stations.