The corrosion of the water wall of a 660 MW supercritical boiler in certain plant in Hunan province was researched in a tube furnace under different kinds of gas mixtures of O2, N2, H2S, CO at 450℃. The function that reveals the relationship of corrosion rate and time was established by measuring the change of the mass of the specimen over time. Meanwhile the effects of atmosphere condition and corrosion time on the high temperature corrosion to water wall were studied by using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The results showed that the corrosion rate increases by 15% when the hydrogen sulfide content in the flue gas grow by 0.01%(?). The corrosion rate continuously decreases with time when the hydrogen sulfide content stays around 0.02%~0.05%(?). The Fe transfers to the surface when FeS accumulated in the composite film with accelerating metal oxidation. The fissure structure on the surface of the composite film forms when the hydrogen sulfide content increases to 0.07%(?) with further accelerating the high-temperature vulcanization and oxidation.