Abstract: Aiming at the phenomenon of cracking and water leakage appearing secondly on convection tube of neighborhood positions in some boiler during operation, testing methods such as chemical composition analysis, mechanical property testing, macroscopic and microscopic examination were applied to identify the cracking and water leakage reasons on boiler convection tube. The results showed that overtemperature operation of local pipe made its strength reduce significantly, and led to cracking and water leakage finally.