Decorating a high-efficiency oxygen evolution reaction (OER) electrocatalyst as a cocatalyst on an α-Fe₂O₃ photoanode is known to be one of the most efficient methods to improve the photoelectrochemical (PEC) water oxidation activity. In our work, different from traditional methods of transition metal sulfide cocatalyst synthesis, an NiFeS_x–decorated Ti-Fe₂O₃ photoanode is synthesized through a simple one-step electrodeposition method, which benefits the interface between Ti-Fe₂O₃ and NiFeS_x. With the help of this excellent OER electrocatalyst, the photocurrent density of the NiFeS_x–Ti-Fe₂O₃ photoanode rises to 3 mA cm⁻² at 1.23 V vs. RHE, which is 2.5 times greater than the photocurrent of Ti-Fe₂O₃. Moreover, the onset potential of NiFeS_x–Ti-Fe₂O₃ shifts negatively by 170 mV compared with that of pure Ti-Fe₂O₃. Furthermore, surface photovoltage spectroscopy (SPV) and transient photovoltage (TPV) techniques and photoelectrochemical impedance spectroscopy (PEIS) were used to analyze the true effects of NiFeS_x as an efficient cocatalyst for enhancing the PEC performance of the NiFeS_x–Ti-Fe₂O₃ photoanode. This work provides a simple method for loading a low-cost and efficient cocatalyst to modify a Ti-Fe₂O₃ photoanode for the PEC water oxidation reaction.