Abstract: In order to find out the leakage cause of a SA210 (A1) high-pressure evaporator tube, chemical composition analysis, tensile testing, metallographic examination and energy spectrum analysis were carried out. The results show that the leakage of the high-pressure evaporator tube was not caused by material problem. The corrosion morphology and X-ray inspection results show that the leakage occurred in the vicinity of the weld heat affected zone. Through the investigation on on-site conditions and morphology analysis on unleaked tube before and after chemical cleaning, pickling simulation test and analysis on sediment at the inner wall, it is found that there is a corresponding relationship between the corrosion characteristics of the inner wall and accumulated water during the period out of service. Picking process didn't cause significant corrosion to the substrate and corrosion occurred mainly before chemical cleaning. The on-site conditions reoccurred by deactivation corrosion simulation test. The results show that the corrosion characteristics are consistent with those of the actual tube on site. Therefore, the water and dirt in part of the tube during construction led to the deactivation oxygen corrosion, which is the main reason for the leakage of the evaporator tube.