In　order　to　investigate　the　defect　effect　on　photocatalytic　performance　of　the　visible　light　photocatalyst,　Zn-Cd-S　solid　solution　with　surface　defects　is　prepared　in　the　hydrazine　hydrate.　X-ray　photoelectron　spectra　and　photoluminescence　results　confirm　the　existence　of　defects,　such　as　sulfur　vacancies,　interstitial　metal,　and　Zn　and　Cd　in　the　low　valence　state　on　the　top　surface　of　solid　solutions.　The　surface　defects　can　be　effectively　removed　by　treating　with　sulfur　vapor.　The　solid　solution　with　surface　defect　exhibits　a　narrower　band　gap,　wider　light　absorption　range,　and　better　photocatalytic　perfomance.　The　optimized　solid　solution　with　defects　exhibits　571　mol　h(-1)　for　50　mg　photocatalyst　without　loading　Pt　as　cocatalyst　under　visible　light　irradiation,　which　is　fourfold　better　than　that　of　sulfur　vapor　treated　samples.　The　wavelength　dependence　of　photocatalytic　activity　discloses　that　the　enhancement　happens　at　each　wavelength　within　the　whole　absorption　range.　The　theoretical　calculation　shows　that　the　surface　defects　induce　the　conduction　band　minimum　and　valence　band　maximum　shift　downward　and　upward,　respectively.　This　constructs　a　type　I　junction　between　bulk　and　surface　of　solid　solution,　which　promotes　the　migration　of　photogenerated　charges　toward　the　surface　of　nanostructure　and　leads　to　enhanced　photocatalytic　activity.　Thus　a　new　method　to　construct　highly　efficient　visible　light　photocatalysts　is　opened.