Abstract: The burst accident of 12Cr1MoVG steel pipe of high temperature superheater of a steam boiler occurred. The causes of the burst were analyzed by means of macroscopic observation, chemical composition analysis, tensile test, hardness test, metallographic examination, scanning electron microscope and energy spectrum analysis. The results show that the fouling of the inner wall caused the superheater tube to run over-temperature for a long time, the material structure was seriously spheroidized, and the mechanical properties were reduced. Under long-term high-load operation conditions, the fouling layer fell off and deposited at the lower elbow, causing serious overheating of the straight pipe section. Under the action of working pressure and thermal stress, the steel pipe swelled and eventually burst.