Abstract: The cracking cause of an oil and gas pipeline were analyzed by means of macroscopic observation, chemical composition analysis, fracture analysis, hydrogen induced cracking test and sulfide stress cracking test. The results show that the pipe cracking had the characteristics of bulging deformation and wall thickness reduction. The fracture showed toughness nests morphology. The cracking mode of the pipeline was overload plastic fracture. The cracking reason was that the pressure of the pipeline suddenly increased, which caused local bulging of the pipeline, resulting in cracking of the pipeline.