Abstract: The leakage reasons of the water-wall tube used for a boiler’s SNCR denitrification were investigated by means of macroscopic and microscopic analysis, mechanical properties test, chemical compositions analysis, metallographic examination, energy disperse spectroscopy analysis and X-ray diffraction analysis. The results indicate that the leakage of the denitrification water-wall tube was caused by the localized corrosive perforation under the corrosive medium of carbamide. The carbamide liquid leaked from the denitrification spaying gun dropping on the high-temperature water-wall tube and the tensile stress at weld toe of the finned tube created the appropriate conditions of medium, temperature and stress for the corrosive leakage.