The invention discloses a preparation method of graphene, which is characterized in that natural graphite used as a raw material is subjected to mechanical stripping under the auxiliary action of graphene quantum dots by using a polar solvent as a dispersion medium to prepare the high-quality graphene. The stripping of the natural graphite and dispersion of the graphene nanosheets in the polar solvent are promoted by utilizing the favorable dispersivity of the graphene quantum dots in the polar solvent and the strong non-covalent bond combination between the graphene quantum dots and graphene/graphene laminae, thereby obtaining the high-quality graphene. According to the invention, the graphene powder is directly obtained from the natural graphite under the condition of not introducing any surfactant, inorganic salt, organic salt or any other impurity. Compared with the existing methods, the method is simple in technique, and can be perform in multiple polar solvents; the maximum yield of the obtained graphene can reach 50%, and the quality is good; the graphene quantum dots used for auxiliary stripping can be recycled; and thus, the method is very suitable for mass preparation of graphene.