For the first time we presented the interfacial charge carrier dynamics for three-component semiconductor-metal-semiconductor Z-scheme nanoheterostructure system. The samples were prepared by selectively depositing a thin layer of Cu2O on the Au surface of Au nanoparticle-decorated NaxH2-xTi3O7 nanobelts (denoted as ST-Au NBs) using the photodeposition method. For ST-Au-Cu2O NB heterostructures, the embedded Au may act as carrier-transfer mediator to promote the electron transfer from the conduction band of ST to the valence band of Cu2O. This vectorial charge transfer would give rise to electron accumulation at Cu2O and hole concentration at ST, which achieved superior charge carrier separation over the two-component counterparts of ST-Au and ST-Cu2O. The quantum size effect was significant in the deposited Cu2O, which was exploited to tune the band structure of Cu2O, modulate the charge carrier dynamics of ST-Au-Cu2O NBs, and thereby enhance the resultant photocatalytic performance. Time-resolved photoluminescence spectra were measured to quantitatively analyze the electron transfer event between ST and Au for ST-Au-Cu2O NBs, which was found dependent on the Cu2O shell thickness. As the Cu2O thickness decreased, ST-Au-Cu2O NBs showed an increased electron-scavenging rate constant due to the increased driving force of electron transfer. The carrier dynamics results were fundamentally consistent with those of the performance evaluation in photocatalysis, in which ST-Au-Cu2O NBs exhibited enhanced photocatalytic efficiency as the Cu2O thickness decreased. Systematic understanding of the interfacial charge dynamics of Z-scheme mechanism shall pave the way for the realization of artificial photosynthesis by using heterogeneous photocatalysts, where the effectiveness of charge separation and the merit of high redox powers are determinant.