Hexavalent chromium poses long-term environmental risks and can cause genetic defects and even cancer in humans，whereas trivalent chromium does not．At present，photocatalytic degradation of hexavalent chromium is considered as a cheap and rapid method． C3N4 is a planar graphene-like material with good photocatalytic performance．By composite copper，zinc，tin and sulfur ( Cu2ZnSnS4 ) ，the composite material with excellent degradation performance was obtained，and the degradation rate reached 95．2% at 5 min．Compared with the single C3N4 and Cu2ZnSnS4，the increase was 4．83 and 1．4 times．