Photoelectrochemistry that use semiconductors to absorb sunlight for water splitting provides an effective method for the development of renewable hydrogen energy in the future. In this paper, a transparent and highly-efficient cobalt-iron oxide (Co₃FeO_x) nano-film was fabricated through hydrothermal method by directional adjustment of atomic ratio to promote the kinetics of BiVO₄ (BVO) photoanode water oxidation. As a result, the Co₃FeO_x-modified BVO photoanode (Co₃FeO_x/BVO) exhibits an impressive photocurrent density of 4.0 mA·cm^-2 at 1.23 V versus reversible hydrogen electrode (RHE), approximately 2.17-fold higher than that of bare BVO, as well as a cathodically shifted onset potential of 320 mV. Transparent catalyst nanolayer structure is clarified by ultraviolet-visible spectroscopy. In addition, the Co₃FeO_x/BVO photoanode has better stability, and there is no obvious activity degradation after 10 hours of reaction. This strategy provides a broad prospect for the use of water oxidation co-catalyst to achieve effective water splitting.