In this work, Cu2O-reduced graphene oxide (rGO) composites were synthesized with tunable Cu2O crystal facets ({111}, { 110} and {100} facets). The degradation performance of methylene blue under visible light was ranked: o-Cu2O{111}-rGO > d-Cu2O{110}-rGO >c-Cu2O{100}-rGO. UV-vis diffuse reflectance and photoluminescence spectra showed that 0-Cu2O-rGO exhibited the enhanced visible-light absorption and the faster charge-transfer rate. Furthermore, X-ray photoelectron spectroscopy and Raman characterizations showed that o-Cu2O-rGO was beneficial for the stabilization of Cu+ species and the formation of oxygen defects. With the help of in-situ electron spin resonance (ESR), more superoxide radicals were detected over o-Cu2O-rGO, which promoted organic pollutants degradation. The above results confirmed that the catalytic behaviors of three Cu2O-rGO composites were related to the electronic structures and interfacial connections. The o-Cu2O{111}-rGO displayed the superior performance, for the highly-active coordinated unsaturated Cu and the intensive interfacial connection, which was beneficial for the rapid the photo-generated electron transfer and the formed active superoxide species. This study showed that engineering the interfacial structures could provide a scientific basis for the design of efficient photo-catalysts. (C) 2015 Elsevier B.V. All rights reserved.