The roles of interface charge transfer and surface proton reduction on photocatalytic hydrogen generation were investigated using Pt cocatalyst on RGO as a model catalyst. The results indicated that the interface charge transfer between reduced graphite oxide (RGO) and Pt nanoparticles (Pt NPs) was more pronounced on photoinduced hydrogen generation over sensitized Pt cocatalyst on RGO than surface proton reduction reaction. The photogenerated electron interface transfer could be modulated by controlling surface potential energy on a selectively exposed Pt facet. By X-ray photoelectron spectroscopy (XPS) and the fluorescence lifetime experiments, we proved that Pt(100) NPs had a noticeably stronger interaction with RGO than Pt(111) NPs, which resulted in a faster electron transfer from RGO to Pt(100) NPs and eventually led to higher activity for hydrogen evolution than Pt(111)/RGO cocatalyst. The XPS results confirmed this interaction difference; that is, the different facets of Pt NPs loading on RGO coresponded to different binding energy. The binding energy of Pt(100) f_7/2 shifted to higher energy side by 0.54 eV on RGO, while the binding energy of Pt(111) f_7/2 shifted up only ∼0.31 eV. The results of fluorescence lifetime verified that the photogenerated electrons transferred faster from RGO to Pt(100) NPs than to Pt(111) NPs, indicating Pt(100) NPs more strongly interacted with RGO. This study disclosed the facet-dependent effect of noble-metal Pt cocatalyst on RGO in photocatalytic water reduction and will give insight into understanding the electron transfer between Pt NPs and RGO.