Abstract: In order to study the effect of pipe diameter increase on the safety and reliability of natural gas pipelines and analyze the feasibility of OD 1 422 mm X80 pipeline program, the risk levels were compared between OD 1 422 mm X80 pipeline with the design factor 0.72 and OD 1 219 mm X80 pipelines with the design factor 0.72 and 0.8 on the basis of pipeline risk assessment theories from the respects of crack arresting toughness, potential hazard influencing area, critical defect size, puncture resistance, failure probability, individual risk and operating risk. Results showed that under the same operation conditions, OD 1 422 mm X80 pipeline with the design factor 0.72 is higher than OD 1 219 mm X80 pipeline with the design factor 0.72 and 0.8 in terms of the critical defect size and the puncture resistance, and lower in failure probability which is caused by external corrosion and equipment impact. However, the radius of potential hazard influencing area is larger. Correspondingly, failure consequence may be increased and the overall risk level may be higher, but their difference is not significant. The research results in this paper provide not only technical support for the design and construction of OD 1 422 mm X80 pipeline engineering, but also a decisive basis for the optimization of large-capacity pipeline programs.