Abstract: This study aims to investigate the passivation behavior and mechanisms of low carbon steel in concrete pore solutions with different pH values. Through open circuit potential, linear polarization resistance, electrochemical impedance spectroscopy and ToF-SIMS analysis, the effect of pH on the passivation behavior of low carbon steel was examined in detail. The results demonstrate that mild steel can spontaneously form a passivation film in concrete pore solutions of any pH value, with the film on its surface undergoing a transition from rapid initial growth to a more gradual stabilization over time. pH is a crucial factor in promoting the passivation of mild steel and shows a positive correlation with the performance of the passivation film. As the pH of the simulated solution increases, there is a tendency for the thickness of the passivation film to increase, resulting in the formation of a more stable passivation layer, thereby enhancing its passivation properties.