Abstract: A series of Cu2O/Agx composite catalysts were synthesized by a liquid phase reduction method. The properties of Cu2O/Agx samples were characterized by XRD, SEM, TEM and DRS analyzing methods. The results indicated that the surface of Cu2O/Ag catalyst were coated by metallic Ag nanoparticles presenting like islands, inducing in evident enhance in plasmon resonance effect and the light absorption in UV, Vis and NIR wavelength regions. Cr(VI) was reduced by Cu2O/Agx composite catalyst in the dark without ultrasonic dispersion, thereinto, Cu2O/Ag0.15 sample shows the strongest reducing capacity in all catalysts. In the presence of 0.01 M citric acid buffer solution (pH=5.0), 100 mg/L Cr(VI) was completely reducd in 30 min in the dark. Meanwhile, the catalytic reduction mechanism of Cr(VI) in Cu2O/Ag composite catalyst system and the effect of citric acid were proposed.