Inspired by the nature photosynthesis, fabrication of Z-scheme system is an effective strategy to enhance the photocatalytic activity, via which photogenerated electrons and holes that take part in the redox reactions can be separated spatially and temporally, while their strong redox capability can still be preserved. It is of great importance to construct good Z-scheme demo systems, and yet a considerable challenge to verify the charge transfer direction, which is vital for designing and fabricating the photocatalytic systems with high efficiency. Here ZnS@ZnO core-shell nanostructures were fabricated via simply annealing ZnS(en)(0.5) precursor, which exhibited superior activity for solar fuel production to ZnS. The Z-scheme mechanism was proposed based on the experimental results of charge transfer study. Direct intimate contact is formed at interface due to in-situ growth with common Zn cation. Specifically, ZnSXO1-X( and/or defects may be formed at the interface, which behave like a mediator in a Z-scheme system. All these account for the observed efficient separation of charge carriers and enhanced activity of photocatalytic reduction.