The separation mechanisms of photogenerated electrons and holes for composite photocatalysts have been a research focus. In this paper, the composite g-C3N4-WO3 photocatalysts with different main parts of C3N4 or WO3 were prepared by ball milling and heat treatment methods. The photocatalytic performance was evaluated by degradation of methylene blue (MB) and fuchsin (BF) under visible light illumination. The photocatalyst was characterized by X-ray powder diffraction (XRD), UV-vis diffuse reflection spectroscopy (DRS), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) methods. The separation mechanisms of photogenerated electrons and holes of the g-C3N4-WO3 photocatalysts were investigated by electron spin resonance technology (ESR), photoluminescence technique (PL), and determination of reactive species in the photocatalytic reactions. When the main part of the g-C3N4-WO3 photocatalyst is WO3 (namely g-C3N4/WO3), the transport process of the photogenerated electrons and holes adopts the generic band-band transfer. Meanwhile, g-C3N4 is covered by WO3 powder, and the role of g-C3N4 can not be played fully. The photocatalytic activity of the photocatalyst is not obviously increased. However, when the primary part of the WO3-g-C3N4 photocatalyst is g-C3N4 (namely WO3/g-C3N4), the migration of photogenerated electrons and holes exhibits a typical characteristic of Z-scheme photocatalyst, and the photocatalytic activity of the photocatalyst is increased greatly. (C) 2014 Elsevier B.V. All rights reserved.