Based on depassivation experiments of steel bar in simulated concrete pore solution， the influences of working area for steel electrode and pH value for simulated concrete solution on open-circuit potential， polarization resistance and corrosion current density during depassivation process were investigated. The critical chloride concentration of steel bar under different conditions of working areas and pH values were determined. The quantitative relationship between the critical chloride concentration and the working area as well as pH value were established respectively. The results show that the critical chloride concentration decreases with the increase of working area of steel electrodes. The critical chloride concentration in terms of free chloride ion concentration ［Cl^-］ increases with the increase of pH value for simulated concrete pore solution， while the critical chloride concentration in terms of ［Cl^-］/［OH^-］ decreases with the increase of pH value for simulated concrete pore solution. Comparing with open-circuit potential and polarization resistance， the inflection point of corrosion current density is more obvious during the depassivation process of steel bar.