The invention discloses a preparation method of a palbociclib intermediate, which uses 5-bromo-2,4-dichloropyrimidine and cyclopentylamine, uses dichloromethane and other solvents and water as solvents, and uses inorganic bases as acid-binding Preparation of 5-bromo-2-chloro-N-cyclopentaline-4 amine, then DIEA is used as an acid-binding agent, DMF is a solvent, and TBAB is a phase transfer catalyst. In the presence of water, a small amount of palladium is used to catalyze, Through normal hexane reflux dehydration, further dehydration ring closure of acetic anhydride obtains 2-chloro-8-cyclopentyl-5-picoline [2,3-D] pyrimidin-7 (8H)-one, the obtained compound is in acetonitrile In reaction with NBS, 6-bromo-2-chloro-8-cyclopentyl-5-methylpyrido[2,3-D]pyrimidin-7(8H)-one is obtained. The method has the advantages of mild reaction, simple and convenient operation, reusable solvent, less environmental pollution, high yield, low cost and high product quality, and is suitable for industrialized production.