Abstract: After operation about 17 520 h, 12Cr1MoVG steel superheater tube used in a boiler of a power station cracked. In order to find the burst causes, failure analysis was carried out. The results show that the pearlite in the matrix turned to spheroidization because the tube used at high temperature over a long period of time, which resulted in the decrease of strength of the tube. Under the environment of high temperature vapor, the oxide scale was easily formed on the inner wall of the tube and then broken off because of vapor washing. Circularly, the thickness of the tube was reduced further and the strength significantly decreased at the two combined action. Corrosion pits were found on inner wall of the tube pits because of the corrosive elements in the vapor, and then, the corrosion pits became crack source as a result of stress concentration. If the stress concentration exceeded the strength of the steel tube at high temperature, the tube would burst.