The corrosion conditions of rebar embedded in the concrete which was immersed in 10% sodium chloride solution(pH=12) for 9 d was studied by using the wire-beam electrode.Through measuring the natural corrosion potential,polarization resistance and polarization electric current,and analyzing the compactness of the concrete near the wire-beam electrode,the pH value of solution and the content of chloride ion,the corrosion conditions of reinforcing steel bar which was caused by heterogeneity in diffusion of chloride ion due to heterogeneity of the concrete was studied.The result shows that the thicker the protective layer of the concrete,the higher the natural corrosion potential of wire-beam electrode,which could alleviate the corrosion of the rebar.It is also found that the pH value is relatively higher and that the content of chloride ion is lower in dense areas of the concrete where the natural corrosion potential is higher,therefore the corrosion of reinforcing steel bar in this area is rather slight.While the other areas where the concrete is not dense,the things are opposite.