The invention discloses a preparation method of a highly stable branch dendritic bromide perovskite quantum dot. The above quantum dot material is CH3NH3PbBr3 wrapped with polyamidoamine dendrimer (PAMAM), and the structural formula of the quantum dot material is PAMAM-CH3NH3PbBr3. The preparation method comprises the following steps: (1) adopting the PAMAM with a carboxyl functional group and n-octylamine as ligands to realize the assisted preparation of a PAMAM-CH3NH3PbBr3 precursor solution; and (2) transferring the precursor solution into toluene, and uniformly shaking the precursor solution and the toluene to form the PAMAM-CH3NH3PbBr3 quantum dot. The method for preparing the perovskite quantum dot through a one-pot technology has the advantages of simplicity, easiness in operation, convenience in raw material supply, completion in general laboratories, and easiness in promotion.