Cl^- and SO₄^2- are most common aggressive ions containing in the seawater which may cause the localized corrosion of reinforcement structures. It is found that a protective passive film will form on the steel surface in the concrete pore solution. The localized breakdown of the passive film caused by the aggressive ions and the carbonation are the main reason for the localized corrosion initiation of reinforcements. In the previous studies, it is found that the performances of the SO₄^2- on the rebar corrosion were quite different in different pH value conditions and the test results did not unify. Therefore, the influence of pH value and the SO₄^2- on the corrosion behavior of Q235B carbon steel in the simulated pore solution was studied using anodic polarization, electrochemical impedance spectra (EIS), Mott-Schottky (M-S) and potentiostatic polarization methods. The anodic polarization curves indicate that when the pH value of the simulated pore solution was higher than 11, SO₄^2- had no damage to the passive film. However, once the pH value of the simulated pore solution decreased to 10, a small amount of SO₄^2- can lead to the breakdown of the passive film and induce pitting initiation. EIS and M-S measurement results suggest that the stability of the passive film would decrease with the decreasing of the solution pH. The concentration of the defect would increase in the passive film due to the pH decrease. The stability reduction and the increase of defect concentration both can lead to the passive film become fragile and more easily to be destroyed by SO₄^2-. Through the potentiostatic polarization test in conjunction with SEM observation, it is found that SO₄^2- can inhibit the growth of the passive film during the initial film formation period and lead to the appearance of metastable pitting corrosion under high pH value conditions. In the low pH value conditions, SO₄^2- could accumulate at the defect of the passive film and lead to stable pitting propagate on the steel surface.