The corrosion behavior of P110S steel in CO2-H2S saturated high-salt aqueous with pH buffer was investigated using an autoclave. SEM, EDS, XRD, and Pourbaix diagrams were used to analyze the corrosion scale characteristics. P110S steel experienced severe localized corrosion in high-salt aqueous containing saturated with CO2-H2S despite the addition of pH buffer. The main component of the corrosion scale was mackinawite and FeCO3. The corrosion scale with mackinawite as the main component was dense and had a good protective effect. The corrosion was very light in the area covered by this corrosion scale. However, this corrosion scale was poorly bonded to the matrix and is prone to partial cracking and peeling, which was the cause of severe localized corrosion of P110S steel.