Abstract: The tough-brittle transition temperature of whole scaledpipelines can be obtained through explosion test on such pipes with premade fractures at low temperature. In the process of test, the fracturing and explosion pressure values are approrimate to that worked out by the theoretical formaula. Whole scaled pipelines may have two kinds of transition temperature, one of starting fracture, the other of extension. The former is determined according to the changing law of f racture toughness in correspondance with explosion temperature. extension transition temperature is in general determined by the temperature corresponding with the percentage of shear fracture opening.