In aqueous ethanol solution, the surface of nano-SiO₂ was modified by silane coupling agent KH560 . And the particle sizes were measured. The effects of nano-SiO₂ content, alcohol percentages and the modification agents on dispersity were discussed. The chromium-free passivation solution was made from the modified nano-SiO₂ dispersions, water polyurethane resin and inorganic constituent compound, and it may be coated on the hot galvanized sheet . Corrosion resistances of nano-SiO₂ modified polyurethane composite passivation film and unmodified polyurethane composite passivation film were characterized by the electrochemical Tafel polarization curves, AC impedances ( EIS) and the neutral salt spray tests. The results may show that compared with the latter the former corrosion resistance have been greatly improved.