Abstract: The introduction of second-phase materials to construct heterojunctions and the addition of co-catalysts can effectively improve the photoelectrochemical performance of semiconductor materials. In this study, Ti₃C₂-WO₃/SrTiO₃ composites were designed and prepared to protect 304 stainless steel (304 SS) by photochemical cathodic protection technology in simulated sunlight environment. The results show that the photoelectrochemical cathodic protection performance of Ti₃C₂-WO₃/SrTiO₃ composites is significantly enhanced. Coupling 304 SS with Ti₃C₂-WO₃/SrTiO₃ composites transfers the potential of 304 SS from −0.13 V to −0.42 V, and the ternary composites produce a photocurrent density 7 times higher than SrTiO₃ alone. The heterojunction electric field formed at the WO₃/SrTiO₃ interface and the addition of co-catalyst Ti₃C₂ synergistically improve the separation efficiency of photogenerated electrons and holes, and improve the photoelectrochemical cathodic protection performance.