The invention belongs to the field of new materials in organic solar cells (OSCs) and perovskite solar cells (PVSCs), and more specifically, relates to a squaric acid high-molecular polymer, and a preparation method and an application thereof. The high-molecular polymer takes a fragment formed by covalent connection of asymmetric squaric acid and indacenodithiophene as a copolymerization unit. Thehigh-molecular polymer has the advantages of simple synthesis process, good light absorptivity and high hole mobility ratio, and can be applied to organic solar cell donor materials and hole-transport materials in trans-perovskite solar cells respectively, and the obtained highest efficiencies are 6.35% and 18.29% respectively.