In this study, the Ag/AgCl/SnO2 composite photocatalysts with diffident molar ratios of Ag/Sn nano-particles were facilely constructed by a precipitation method. The samples were characterized by X-ray diffraction patterns (XRD), UV-Vis diffuse reflectance spectra (DRS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), electron spin-resonance (ESR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The Ag/AgCl/SnO2 composite with molar ratio of Ag/Sn = 7% display the highest photocatalytic activity under the simulated sunlight irradiation. The active free species trapping and NBT experiments indicate that the photo-induced charges separation and transfer result in the efficient formation of center dot O-2(-) in the composite system. Based on all the experimental results, a Z-scheme charge separation and transfer mechanism was proposed to explain the efficient formation of center dot O-2(-) over Ag/AgCl/SnO2 composites under the simulated sunlight irradiation. (C) 2017 Published by Elsevier B.V.