The invention relates to a preparation method of a polymeric phase-change material, comprising: using 1, 2 or 3 of (meth)acrylate poly(ethylene glycol) n-alkyl ether ester as a raw material, wherein the (meth)acrylate poly(ethylene glycol) n-alkyl ether ester has a structural general formula of CH2═C(CH3)—COO(CH2CH2O)mCnH2n+1 or CH2═CH—COO(CH2CH2O)mCnH2n+1, m=1 to 100, and n=10 to 50; washing the raw material with a solution of sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate having a mass percentage of 1% to 10% to remove a polymerization inhibitor, and subjecting reduced-pressure distillation, and then to a polymerization reaction by adopting one of the following process; 1. polymerization reaction initiated by irradiation; 2. polymerization reaction initiated by an initiator; 3. polymerization reaction in a solvent; after the polymerization reaction is completed, adding a precipitating agent to precipitate the polymeric phase-change material from the solution, and then washing with deionized water and dried, to obtain a polymeric phase-change material as a powder to block.