Abstract: The influence of cement composition on the corrosion of steel bar in concrete is studied in this paper. The acceleration test is designed according to the natural mechanism of steel bar corrosion in concrete, and several electrochemical methods are used in the study. The results of research show that the cement composition has a great influence on the corrosion of steel bar in concrete. The concrete produced with blended cement can delay the corrosion time of steel bar and prolong the beginning time of steel bar corrosion. The dense effect and absorption effect on Cl- can improve the microstructure of interface between the concrete and steel bar and reducing Cl- concentration effectively, thus reduce the corrosion rate of steel bar in concrete.