First principles calculations were performed to cast insight into the mechanism of the improvement of O-2 reduction reaction (ORR) activity by Zn and H interstitials on the anatase TiO2 (101) surface. For the Znmodified anatase TiO2 (101) surface, both surface and subsurface Zn interstitials could contribute to O-2 adsorption and dissociation, but the dissociation barriers of O-2 molecules are still too high, which limits the ORR activity. After a H adatom is introduced onto the Zn-modified anatase TiO2 (101) surface, the highest energy barriers are greatly reduced compared with those of the Zn-modified surface. Meanwhile, it is observed that the dissociation barriers decrease almost linearly with the increase of the charge difference of adsorption O-2 between initial and transition state configurations. Specifically, subsurface Zn and surface H interstitials facilitate O-2 dissociation and subsequent oxidation reactions, and further frequency analysis shows that these dissociation processes are frequent even at the room temperature of 300 K. In a word, this work provides a theoretical support to design a high ORR activity catalyst of the TiO2 nanocrystal comparable to precious Pt catalysts.