Abstract: Galvanized steel sheet was blackishgreen colored passivated in tetracid solution system with acetic acid solution as stabilizer and silver salt solution as toner.The micro-morphology of the film before and after passivation was observed by SEM.The composition of the film was tested by EDS and its phase compositon was analyzed by XRD.The corrosion resistance of the passivated film was studied by neutral salt spray test.The results show that the surface of the specimen without passivation film was complete consecutive and coarse electrodeposited zinc coating.The surface became homogeneous and smooth,and turned blackishgreen but had chap structure.The film was composed of Cr,O,P,S,Zn and a small amount of Fe element.There were phases in the film,including CrPO4,Cr(OH)3,CrOOH,Cr2O3,Zn(OH)2,2ZnO·CrO3·H2O,Zn3(PO4)2·4H2O and Ag.Zinc coating,passivation film and Fe matrix combined closely,and no defects appeared such as crack.The passivation film could endure neutral salt spray test for 400 h,which met the demands of national and enterprise standards.