Corrosion studies in s-CO2-saturated aqueous systems draw less attention compared to wet s-CO2-rich systems. The current database cannot suffice the clarity for the effect of the aqueous component on the steel corrosion, e.g., the influence of Cl-ion on the dissociation of CO32− on the steel surface. In the present work, we explored the influence of Cl ion and temperature variations on the corrosion of X65 steel in supercritical CO2 (s-CO2) saturated aqueous environments. Corrosion experiments were conducted on X65 steel in s-CO2-saturated 3.5 wt.% NaCl solutions at 8 MPa with varying temperatures of 50, 75, and 100 °C. X65 steel exhibits significantly lower CRs in s-CO2 saturated salt (NaCl-containing) aqueous solution compared to those in DI water. After exposure to s-CO2 saturated DI water at 50 °C for 96 hours, a loose and cracked FeCO3 film was observed on the X65 steel, resulting in the highest CR of 5.10 mm/y, in contrast to the samples exposed to the s-CO2 saturated salt solution at 50 °C (1.47 mm/y), 75 °C (1.01 mm/y), and 100 °C (0.93 mm/y).