For water oxidation reaction, it involves multi-electron reaction, which is the rate-determining step for the photocatalytic water splitting, meaning the photocatalytic water splitting reaction kinetic is limited by water oxidation reaction. Here, we demonstrate that the O-2 evolution reaction (OER) cocatalyst (CoOx) can dramatically improve the OER performance of the hexagonal alpha-Fe2O3 photoharvester. Although the pure hexagonal alpha-Fe2O3 is inert for water oxidation, the photocatalytic O-2 evolution rate of 5% CoOx /alpha-Fe2O3 is up to similar to 195.19 mu mol/g/h. The enhanced photocatalytic water oxidation performance can be ascribed to the effective separation of the photogenerated electron-hole pairs of alpha-Fe2O3 and the high transfer kinetics of the holes. The ESR results show that the introduction of CoO x does enhance the transfer and separation efficiency of the photogenerated carriers of the hexagonal alpha-Fe2O3. Additionally, the photocatalytic mechanism was also researched in detail.