The invention discloses a preparation method of a UV monomer for paint. According to the preparation method, lactate and acrylic acid are taken as the raw materials, hydroquinone is taken as the polymerization inhibitor, a solid super acid is taken as the catalyst, anhydrous alcohol is taken as the solvent of polymerization inhibitor, the acrylate-lactate UV monomer is prepared through an esterification reaction, the mole ratio of acrylic acid to lactate is 1.15-1.30:1, the polymerization inhibitor (hydroquinone) accounts for 0.03 to 0.05% of the total weight, the catalyst (solid super acid) accounts for 3 to 5% of the total weight, the lactate is methyl lactate or ethyl lactate, and the acrylate-lactate UV monomer is acrylate-methyl lactate or acrylate-ethyl lactate. The UV monomer prepared by the provided preparation method has the advantages of low production cost, no toxicity, and good performance, and can replace butyl acrylate.