The semiconductor based photocatalytic water splitting is a promising approach for the production of environmentally friendly, clean, and cost-effective hydrogen fuel by utilizing the solar energy. Graphitic carbon nitride (g-C3N4) has emerged as an excellent material to produce hydrogen via photocatalytic water splitting reactions, however the limited visible light absorption and fast charge recombination restricts the further real practical applications. Fabrication of multicomponent g-C3N4 based heterostructured photocatalytic system is an effective strategy to enhance the charge separation and thereby photocatalytic efficiency. Here, a new g-C3N4-Au-In2O3 ternary system with efficient photogenerated charge carrier separation is successfully designed. The morphology, structure, phase and electronic environments of g-C3N4, Au and In2O3 in the composite were studied by different characterization methods. As expected, the optimized g-C3N4-Au-In2O3 catalyst shows excellent photocatalytic H-2 evolution rate. The improved photocatalytic H-2 evolution rate could be attributed to the formation of heterojunctions between g-C3N4, Au and In2O3 components; improved visible light harvesting via surface plasmon resonance (SPR) effect of metal Au nanoparticles (NPs); and effective photogenerated electron-hole pairs separation. The proposed work is expected to provide a new concept to fabricate g-C3N4 based ternary heteronanostructures with metal NPs and metal oxide semiconductors not only to a photocatalytic applications but also opens up to variety of optoelectronic applications.