Abstract: A 110-level oil pipe in Shunbei Oil and Gas Field cracked. By analyzing the service environment, crack morphology, chemical composition, and mechanical properties of the cracked oil pipe and comparing it with the uncracked oil pipe under the same working conditions, the cause of the cracking of this oil pipe was analyzed. The results show that the cracks propagated from the outer surface to the inner surface, exhibited dendritic branching and discontinuous characteristics, and were a typical morphology of hydrogen sulfide stress corrosion cracking. Cracked oil pipes were more sensitive to stress corrosion cracking caused by hydrogen sulfide. Compared with uncracked oil pipes, the tempered martensite structure of cracked oil pipes was more prone to stress corrosion cracking due to the high proportion of grain boundaries, high dislocation density, and high material hardness and strength. When quenching and tempering oil pipes, the tempering temperature should be increased as much as possible to reduce the hardness and strength of the material in order to improve the material' s ability to resist stress corrosion and cracking.