Abstract: The principle to rationally choose the steel pipe for long-distance oil & gas pipeline system is not only very important for the safe operation of pipeline systems, but also can save the investments in pipeline construction. The traditional principle in determing the wall thickness given in the relevant standards and that of in harsh environments have been described. The feasibility in selecting wall thickness with 0.8 strength design factor in sparsely populated areas has been analyzed. Considering the manufacturing limitation in thick-walled steel pipe, the availability to cut down the wall thickness in harsh environments and the fracture mechanics limitation in the available wall thickness of pipe material have been researched.By analyzing the fracture mechanics limitation of pipe material and the project case with the calculation validation, the reference values of theory wall thickness suitable for different grades of steel pipe for high-pressure and large-diameter pipeline have been obtained.