Abstract: The composition and structure of passive film formed from CrO₃-H₃PO₄SiO₂, systems on galvanized steel sheet were inveshgated, the corrosion resistance and its protective causes of the film were also discussed. The experimental results showed thatthe film is a thick type of complex conversion coating with gelatinous net structure containing CrO₃, Cr(OH)₃, CrOOH, ZnCrO₄, ZnSiO₃, Zn₃(PO₃)₂, CrPO₄ and SiO₂, etc. The white rust-resisting property of the film is of three times better than that of film formed from CrO₃-SiO₂, systems because of good shielding and inhibiting.