The invention provides a method for preparing a large-sized perovskite CsPbBr3 hexagonal-round piece with a quantum effect through low-temperature synthesis. The method comprises the following steps: preparing a mixed precursor solution containing Cs-OA and Pb-OA; heating to dissolve TBABr into octadecene, and adding oleic acid and oleylamine as a surface ligand, so as to obtain a bromine-containing mixed solvent; and rapidly stirring and mixing the mixed precursor solution with the bromine-containing mixed solvent at a certain temperature, so as to obtain the large-sized perovskite CsPbBr3 hexagonal-round piece with the quantum effect. The perovskite CsPbBr3 hexagonal-round piece prepared by virtue of the preparation method is low in synthetic temperature and convenient to apply, has a large size and adjustable quantum performance and can be applied to the fields of solar cells, photoelectric detectors, light emitting diodes and the like.