Abstract: In order to find out the reasons for the failure of the insulating joint in gas pipeline, it was studied by nondestructive testing, insulation performance, hydraulic pressure and gas tightness test, anatomical analysis, and metallographic analysis. The results showed that: the insulation resistance was unqualified, and a large number of bubbles ran over from the sealing filler section during the gas tightness test. The main reason for the leakage of the insulating joint was that the actual structure of the insulating joint did not meet the requirements of integral insulating joint under SY/T 0516-2016 Technical Code for Insulating Joint and Insulating Flange, and U-shaped seal ring was replaced by O-shaped seal ring; moreover, the O-shaped seal ring and rectangular sealing groove were not processed as specified, which greatly reduced the sealing performance of the insulating joint, leading to the failure of the insulating joint.