Comparative analyses are adopted to examine the influences of Cl- on the degradation of the film on Alloy 690TT in high-temperature water. According to the results of surface analyses and TEM, the composition and structure of the oxide film formed in a chloride solution are determined. Unlike the duplex layer oxide film formed on the sample in pure water, a thinner and monolayer Cr-rich oxide scale with several little corrosion pits on the surface is formed, which is closely related to the adsorption of Cl- ions due to their affinity to material surface and the selective dissolution of Ni-rich oxides.