The invention discloses a method for preparing Palbociclib (I). The preparation method comprises the steps of: causing a ring-closing reaction of 2-acetyl-2-butenoic acid methyl ester and malononitrile to occur in an alkaline condition to generate 1,4,5,6-tetrahydro-2-methoxyl-4-methyl-5-acetyl-6-oxy-3-pyridine carbonitrile (II); causing a substitution reaction of the intermediate(II) and halogenated cyclopentane(III) to occur under the effect of acid binding agent to generate N-cyclopentyl-1,4,5,6-tetrahydro-2-methoxyl-4-methyl-5-acetyl-6-oxy-3-pyridinecarbonitrile (IV); causing a condensation reaction of the intermediate(IV) and N-[5-(1-piperazinyl)-2-pyridinyl]guanidine (V) to occur to generate 6-acetyl-8-cyclopentyl-5,8-dihydro-5-methyl-2-[[5-(1-piperazinyl)-2-pyridinyl]amino]-pyrido[2,3-d]pyrimidin-7(6H)-one (VI); and causing a dehydrogenation reaction of the intermediate(VI) and sodium selenate to occur to prepare Palbociclib(I).The preparation method has readily available raw materials and a simple process, is economical and environmentally friendly, and is suitable for industrial production.