Abstract: A horizontal tube burst accident occurred in Q245R steel boiler tube of a company after only 8 months of service. The burst causes of the boiler tube were analyzed by means of macroscopic observation, chemical composition analysis, hardness test, metallographic examination, scanning electron microscope analysis and X-ray diffraction analysis. The results show that there were many impurities such as NaCl and Na₂CO₃ in the steam passing through the Q245R steel boiler tube, which made the tube corner blocked and narrowed. The steam velocity and temperature in the front section of the tube were abnormal. Under the action of high temperature, high pressure and corrosive medium, the inner wall of the tube was continuously oxidized, and the tube wall was thinned and decarburized. The strength of the tube was greatly reduced, which was not enough to bear the working pressure, and finally the tube burst.