The invention discloses a passivating agent for a hot-dip galvanized steel plate. The passivating agent for the hot-dip galvanized steel plate comprises, by weight, 25-48 parts of trivalent chromium compounds, 12-24 parts of sodium hypophosphite, 8-18 parts of sodium sulfate, 6-10 parts of sodium fluorosilicate, 18-25 parts of cobalt chloride, 10-15 parts of boric acid, 20-30 parts of organic carboxylic acid, 1-3 parts of sodium dodecyl benzene sulfonate, 10-20 parts of glycerin and 40-60 parts of deionized water. The passivating agent for the hot-dip galvanized steel plate has good stabilityand good dispersion uniformity, and is used for achieving passivation of the hot-dip galvanized steel plate. A utilization method is high in passivating efficiency, an obtained passive film is high inbinding force, smooth in surface and good in compactness, the thickness of the passive film can range from 5mg / m2 to 12mg / m2, and the passive film is high in rigidity and wear resistance. A preparation method of the passivating agent is simple, green and environmentally friendly, accords with the ideas of safety and environmental protection in China, is free of the investment of large equipment,is low in preparation cost and suitable for industrial production, and is worth popularizing.