Abstract: By means of macroscopic examination, chemical composition analysis, metallographic examination, hardness testing, SEM analysis, EDS analysis and XRD analysis, the corrosion reason for the thermal storage element at cold end of air preheater of a 600 MW subcritical boiler was analyzed. The results showed that the corrosion of the thermal storage element was low temperature corrosion happened at flue gas with SO2/SO3. Some preventive measures for the thermal storage element corrosion were brought forward.