To obtain a microscopic explanation on the difference of oxygen reduction reaction activity on different Pt low index surfaces, we simulated competitive adsorptions of O-2 and OH on four Pt low index surfaces. Firstly, all possible chemical adsorption configurations of the O-2 and OH molecules on the three surfaces were acquired through density functional theory. The distribution of these configurations on the different surfaces was collected from Monte Carlo simulations. Our results demonstrated that the adsorption energy order of O-2 on different surfaces was (110)(1 x 2) > (110) > (100) > (111) and that the adsorption energy order of the OH molecules on Pt surfaces was the same. Considering the competitive adsorption of O-2 and OH on Pt surfaces, the final O-2 adsorption efficiencies order of three surfaces was (111) > (110) > (100) > (110)(1 x 2), which was consistent with the experimental activities of oxygen reduction. Our study provided theoretical references for previous experimental studies and had important significance for the understanding of oxygen adsorption on Pt surfaces. (C) 2016 Elsevier B.V. All rights reserved.