Exploration of highly efficient and stable photocatalysts for water splitting has attracted much attention. However, developing a facile and effective approach to enhance the photocatalytic activity for practical applications is still highly challenging. Herein, we report a newly-fabricated perovskite oxide (Pr0.5(Ba0.5Sr0.5)0.5Co0.8Fe0.2O3) decorated with Au ultrafine nanoparticles for photocatalytic water splitting. An exceptionally high hydrogen evolution rate of 1618 μmol g-1 h-1 was achieved (under 2 h illumination) when the Au mass loading was optimized to 9.3 wt%, which is 540 times higher than that of the pristine one. The splendid photocatalytic activity of the sample was attributed to plasmon-excited hot electron injection from Au to Pr0.5(Ba0.5Sr0.5)0.5Co0.8Fe0.2O3 (PBSCF) under illumination. The finite-difference time-domain simulations (FDTD) demonstrated that the localized strong electric field formed at the interface between Au and PBSCF under illumination, enables the hot electrons to be energetic and make the injection possible.