Efficient charge separation is essential for improving the photo-conversion efficiency in both photocatalytic and photoelectrochemical (PEC) water splitting. Herein, we have demonstrated the selective spatial-construction of Au nanolayer and SrTiO₃ nanocubes on inner and outer surfaces of TiO₂ nanotubes for enhancing the charge separation and PEC activity. More specifically, the outer SrTiO₃ nanocubes with a spontaneous ferroelectric polarization could effectively engineer the electrical band bending of TiO₂ nanotubes, facilitating hole transfer to the electrode/electrolyte interface for water oxidation. Meanwhile, the inner Au nanolayer with a favorable plasmonic electric-field induced by the visible light promotes charge separation and rapid electron transfer to the counter electrode for hydrogen generation. Benefiting from the spatial dual-electric fields, this SrTiO₃/TiO₂/Au ternary-photoanode exhibits a significantly enhanced photocurrent density of 2.11 mA cm^-2 at 1.23 V (vs. RHE), which is nearly 3.5 times higher than that of the pristine TiO₂ nanotube arrays. Additionally, a low onset potential (~0.17 V_RHE) for water oxidation as well as an excellent PEC stability has also been achieved. These demonstrations may provide a new strategy toward the rational construction of highly efficient PEC water splitting systems.