Copper modification is an efficient way to enhance the photocatalytic activity of ZnS-based materials; however, the mechanisms of Cu2+ surface and bulk modifications for improving the activity are quite different. In this work, two different synthetic pathways were devised to prepare surface and bulk Cu2+-modified ZnxCd1−xS photocatalysts through cation-exchange and coprecipitation methods, respectively. Different Cu2+ modifications brought different effects on the phase structure, morphology, surface area, optical property, as well as the photocatalytic H2-production activity of the final products. The optimized Cu2+-surface-modified ZnxCd1−xS photocatalyst has a high H2-production rate of 4638.5 μmol h−1 g−1 and an apparent quantum efficiency of 20.9 % at 420 nm, exceeding that of Cu2+-bulk-modified catalyst at the same copper content. Cu2+ surface modification not only brings a new electron-transferring pathway (interfacial charge transfer), but also produces new surface active sites for H2 evolution, reducing the recombination rate of photogenerated charge carriers.