The invention relates to a water-based strong-weather-resistant self-repairing two-component polyurethane topcoat and a preparation method thereof. The topcoat is prepared by mixing a mixture of a group A and a mixture of a group B, wherein the mixture of the group A comprises a water-based hydroxyl acrylic emulsion, a co-solvent, a water-based ultraviolet light absorber, a water-based oilfield fluorescent shielding agent, a neutralizer, a defoaming agent, a dispersant, a pigment, a levelling agent, a substrate wetting agent, deionized water and a thickening agent; and the mixture of the groupB comprises aliphatic isocyanate and an ester organic solvent, and a mass ratio of the mixture of the group A to the mixture of the group B is (4.5-5.5):1. The preparation method comprises the following steps: mixing 50-70% of the deionized water, 40-60% of the neutralizer, the defoaming agent, the dispersant, 15-25% of the co-solvent and the pigment, performing grinding to obtain pre-stage slurry, mixing the water-based hydroxyl acrylic emulsion, and the remaining deionized water, neutralizer and co-solvent, adding the pre-stage slurry into the mixed material, performing mixing, adding the water-based ultraviolet light absorber, the water-based oilfield fluorescent shielding agent, the substrate wetting agent and the levelling agent, adjusting viscosity by using the thickening agent to obtain the mixture of the group A, preparing the mixture of the group B, and mixing the mixtures of the group A and the group B before the topcoat is used.