Utilization of solar energy to split water via photoelectrochemical (PEC) technique is a desirable technology to address the development of sustainable carbon-free energy source. The key challenge of this advanced technique is to design a photoelectrode with both high solar to chemical efficiency and fast charge transfer and separation efficiency. Herein, the core-shell heterostructure of TiO2@PCN (P doped g-C3N4) decorating with Au nanoparticles (Au NPs) photoanode (Au/TiO2@PCN) is successfully fabricated for high-efficiency PEC water splitting. The resulting integrated Au/TiO2@PCN photoanode exhibits significantly enhanced PEC activities both in UV and visible light region with AM 1.5 G irradiation (100 mW cm−2). Each component of Au/TiO2@PCN plays a vital role in promoting the PEC performance. The TiO2@PCN core-shell heterostructure could remarkably facilitate the charge transfer and separation efficiency with the effect of an internal built-in electric field. The introduction of Au NPs could further enhance the charge transfer efficiency and improve the PEC activity of TiO2@PCN in visible light, which is attributed to the localized surface plasmon resonance (LSPR) effect. Accordingly, the Au/TiO2@PCN presents pronounced photocurrent density of 2.03 mA cm−2 (1.23 V vs. RHE), which is four-fold higher than that of TiO2 NRs (0.51 mA cm−2). This work supports a new approach to combine the advantages of the core-shell heterostructure and the LSPR effect of noble metal for high-performance PEC water oxidation.