The invention relates to a preparation method of a polymer heat-storage material containing both-branch Azobenzene side groups, wherein both-branch Azobenzene, which are taken as the side groups, are grafted on alkyl chains, the energy of polymers under illumination can be stored and released by utilizing the acting force among molecules and the cis-trans isomerism of Azobenzene. Firstly, 4-aminoazobenzene reacts with methylacryloyl and trimethyl-1, 3, 5-benzene tricarbonic acid to synthetize Azobenzene, and then Azobenzene is polymerized with the alkyl chains. Compared with Azobenzene micromolecules, the obtained polymer material containing the both-branch Azobenzene side groups has great improvement in an energy value and a half-life period, and the energy density of the polymers is 40Wh/kg; the preparation is easy, and a new method and though are proposed for effective utilization of solar energy; the preparation method is beneficial to heat storage of the solar energy.