The work aims to improve corrosion resistance of Cr III-based iridescent passivation film on zinc coatings by preparing a fine sealant. Principal raw materials of sealing agent were as follows: NaF, Na2SiO3 and OP. The corrosion resistance of Cr III-based iridescent passivation film subject to sealing treatment was studied by 5% lead acetate drop method. Formulation of the sealant was discussed; effects of such process conditions as sealing time, process conditions baking temperature and baking time on corrosion resistance were analyzed; the sealing process was optimized by performing an orthogonal test, so as to determine passivation process specification for sealants with NaF and Na2SiO3 as main salts. The sealant composition obtained was: NaF of 0.2 mol/L, Na2SiO3 of 0.05 mol/L and OP of 1 mL/L. The duration of lead acetate drop experiment might amount to 900 s provided with NaF of 0.2 mol/L, Na2SiO3 of 0.05 mol/L, immersion time of 20 min and baking temperature of 80 ℃. After being sealed, the film is iridescent and bright, and is provided with better corrosion resistance.