Abstract: In the process of anti-wear and explosion-proof inspection of water wall tubes in a power plant, it was found that the wall thickness of a large number of water wall tubes was abnormally thinned. The causes of abnormal wall thickness thinning were analyzed by means of macroscopic observation, chemical composition analysis, mechanical property test, metallographic examination, scanning electron microscopy and energy spectrum analysis. The results show that the main reason for the abnormal thinning of the water wall tube to the fire side was the high temperature corrosion of the sulfide on the fire side tube wall, which eventually led to the abnormal thinning of the water wall tube wall thickness.