The photocurrent has been regarded as the most efficient method to evaluate the photocatalytic activity of composite photocatalyst. A relationship is commonly recognized: the higher the photocurrent is, the higher the e−–h+ separation efficiency is, and thus the higher the photocatalytic activity is. In this paper, we use the TiO2/WO3 composite as a model heterojunction system to argue about this viewpoint, and try to explore a more comprehensive relationship. Our res...