Abstract: The leakage reason of bursted water screen tubes of boiler cold ash bucket were analyzed by means of macroscopic examination, metallographic examination, chemical compositions analysis and SEM analysis. The results reveal that because the high-heat slagging attached to the tubes during period of the boiler operation, the water screen tubes appeared local overheating on the fired-side, which decreased the mechanical properties of the tubes, caused creep bulge deformation, and finally resulted in the leakage of the water screen tubes.