The invention relates to the field of waterborne coatings and particularly discloses a finishing coat of a waterborne coiled steel coating and a preparation method of the finishing coat, wherein the finishing coat of the waterborne coiled steel coating comprises the following components: a waterborne polyester resin, a rust-proof sizing agent, an amino resin, an acid catalyst, a wetting agent, a levelling agent, a defoamer, an adhesion promoter, a wetting dispersant, an anti-settling agent, a PH regulator, a cosolvent and water. the provided finishing coat of the coiled steel coating is a waterborne product, the VOC (volatile organic compounds) content is very low, the environment pollution is small, the performance of a T-bend is greatly improved, the T-bend does not crack in winter and is anti-sticking in summer, and the physical and mechanical properties equivalent to those of the solvent based coating are achieved.