Abstract: The corrosion behavior of two types of casing steel (1Cr and N80) in formation water at different temperatures was compared and studied through dynamic corrosion tests. The corrosion features under different conditions were characterized in detail using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and confocal laser microscopy (CLSM). The results show that at medium temperature and low CO₂ partial pressure (50 ℃, 0.30 MPa), N80 steel had a higher corrosion rate and more severe pitting corrosion compared with 1Cr steel. At higher temperatures (100, 114 ℃) and CO₂ partial pressures (0.63, 0.73 MPa), the corrosion rate of 1Cr steel was about three times that of N80 steel, showing severe mesa corrosion, while the lower average corrosion rate of N80 steel was low due to its film-forming advantage, and the substrate had no obvious pitting characteristics. The composition and physicochemical properties of the product film have a significant impact on the corrosion behavior of casing steel. 1Cr steel exhibits superior performance under the environment of shallow wellbore. However, it is not recommended to use this steel in the deep wellbore, and appropriate materials need to be carefully selected.