Abstract: The choke line of an oil well in an oilfield bursted during the sidetracking process. The reason for bursting of the choke line was analyzed by macromorphology observation, non-destructive testing, chemical composition analysis, mechanical performance testing and fracture morphology observation, as well as internal pressure resistance checking of the burst choke line. The results show that before being used this time, the external wall of the choke pipeline with axial penetration cracks was repaired by welding treatment. The thickness of the repairing weld was very small, and much less than pipeline wall thickness, resulting in the bursting failure during sidetracking because of insufficient bearing capacity of the pipeline. Meanwhile, the poor toughness and impact performance of the pipeline promoted the occurrence of brittle fracture.