The invention relates to a star oligomer for a high-solid coating and a preparation method of the star oligomer. Tris (2-hydroxyethyl) isocyanurate and an epoxy compound serve as raw materials, and the star oligomer for the high-solid coating is synthesized. The synthesis method includes the steps: mixing the tris (2-hydroxyethyl) isocyanurate and the epoxy compound and then heating and stirring mixture; adding catalysts after the tris (2-hydroxyethyl) isocyanurate is melted to obtain the star oligomer. The star oligomer has the advantages that the solid content of the star oligomer is higher than 85%, the star oligomer is low in viscosity, usage of solvents can be decreased, the synthesis method is simple and environmentally friendly, by-products are avoided, and removal of the catalysts is omitted.