The photoelectrochemical (PEC) oxygen evolution reaction over a photoanode is a promising process for renewable energy. The fascinating properties of graphic carbon nitride (g-CN) in water splitting make the photoelectrode engineering of it for PEC use quite meaningful. In this work, we report the fabrication of the core-shell-structured TiO2/g-CN composite film by hydrothermal growth for TiO2 nanorod arrays and solvothermal growth for the g-CN layer. Herein, TiO2 is used as an effective electron-transfer layer, and g-CN is used as a visible light absorption layer. Different reaction conditions were investigated in order to obtain the uniform TiO2/g-CN nanorod core-shell structure. Outstanding photoelectrochemical performances of the optimized composites were obtained compared to that of pristine TiO2 or g-CN because the high-quality heterojunction between g-CN and TiO2 turned out to effectively reduce the recombination of charge carriers and improve the photoelectric conversion ability. Thus, the photocurrent density under visible light of TiO2/g-CN reached 80.9 μA cm-2, which is 21 times that of g-CN under 0.6 V (vs SCE). Finally, a systematic photoelectrocatalytic mechanism of charge carrier migration and the recombination path in the TiO2/g-CN nanorod core-shell heterojunction was proposed, which can be considered to be a probable explanation of efficient PEC performance.