The invention relates to a
chromium-free composite passivator for a hot-dip galvanized steel sheet. The passivator is prepared from the following raw materials in percentage by weight: 2.20-2.30% of water-base resin, 2.60-2.65% of main salt compound, 0.10-0.15% of organic
silane, 0.07-0.09% of
sulfate, 0.11-0.13% of inorganic
zircon salt, 0.09-0.12% of inorganic acid and the balance of water. A preparation method of the passivator comprises the following steps: firstly, dissolving the organic
silane in water; stirring till the organic
silane is fully dissolved and adding the main salt compound; after the main salt compound is dissolved, adding the inorganic acid to measure the pH value; then, adding the
sulfate and the inorganic
zircon salt in the stirring state; after the
sulfate and the inorganic
zircon salt are fully dissolved, adding the water-base resin; stirring till the water-base resin is fully dissolved; adjusting the pH value to 3-4 by virtue of
ammonium water; and standing for later use. An application method of the passivator comprises the following steps: firstly,
degreasing the hot-dip galvanized steel sheet by virtue of an alkaline degreaser during use; then, respectively washing by using
tap water and deionized water; and after
drying,
coating the composite passivator on the surface of the hot-dip galvanized steel sheet. The passivator provided by the invention is free from
chromium and non-toxic and harmless. The thickness of a
passivation film can reach 8-1.0mg / m<2>, and the
corrosion resistance is close to that of a
hexavalent chromium passivating liquid.