Abstract: The water wall tube burst accident occurred many times in a thermal power plant. The reasons for the explosion of water wall tube were analyzed by macroscopic observation, chemical composition analysis, mechanical property testing, corrosion product analysis, scanning electron microscopy analysis and metallographic examination. The results show that the positions of the burst pipes were all located on the windward surface of the water wall tube, and there were corrosion grooves on the inner surface of the steel pipes. There were hard and brittle corrosion products in the grooves, and intermediate products such as NaFeO₂ and Na₂FeO₂ were detected in the corrosion products, indicated that the cause of the burst pipes of the water wall tube was stress corrosion cracking caused by alkali corrosion.