The work aims to study the corrosion behavior of low Cr steels (3%~9%) in CO2/H2S environment at 60 ℃. Three kinds of low Cr steels were heated to 900 ℃ and then water-cooled for 40 minutes. CO2/H2S corrosion tests were carried out to 3Cr-H, 5Cr-H and 9Cr-H steel samples in an autoclave. Morphologies, compositions and phase of corrosion products were analyzed by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD). The corrosion rates of 3Cr, 5Cr and 9Cr steels were 0.0443, 0.0372 and 0.006 mm/a, respectively. The corrosion rates decreased with the increase of Cr content. The corrosion rates of 3Cr-H, 5Cr-H and 9Cr-H steels were 0.1527, 0.0445 and 0.007 mm/a, respec-tively. The corrosion rates also decreased with the increase of Cr content. The corrosion rate of 3Cr-H steel was 3.4 times that of 3Cr steel, and the corrosion resistance changed obviously. The corrosion rate of 5Cr-H steel was 1.19 times that of 5Cr steel. The corrosion rate of 9Cr-H steel was almost the same as that of 9Cr steel. The corrosion products of the six materials were all FeS compounds, and no typical FeCO3 crystals (CO2 corrosion product) were found. The corrosion products of 3Cr, 5Cr, 3Cr-H and 5Cr-H steels were of double-layer structure, while those of 9Cr and 9Cr-H steels were of single-layer structure. Heat treatment does not affect the trend between the content of Cr and corrosion rate. The higher the content of Cr in the matrix is, the greater the concentration of Cr in the corrosion product film, which helps to reduce the corrosion rate; Heat treatment has the most significant effect on the microstructure and corrosion behavior of 3Cr steel, which not only aggravates the uniform corrosion, but also promotes pitting corrosion. This is due to the precipitation of second phase carbides containing Cr in the microstructure after heat treatment, thus resulting in the phenomenon of poor Cr in some areas.