Abstract: The invention relates to the field of nano materials, in particular to biomass-based high-efficiency fluorescent graphene quantum dot and preparation method thereof. Method for preparing biomass-based high-efficiency fluorescent graphene quantum dots includes hydrothermal reaction of composite carbon source, nitrogen source, polyvalent metal ion and water. The method for preparing a biomass-based high-efficiency fluorescent graphene quantum dot includes the following steps: (1) Mixing the composite carbon source and the nitrogen source, and then adding water, stirring and dissolving to obtain a mixture A; (2) Adding polyvalent metal ions to the mixture A, and after stirring, heating and reacting to obtain a crude product; (3) The crude product is purified by dialysis to obtain a purified product. The biomass-based high-efficiency fluorescent graphene quantum dot of the invention has the characteristics of high fluorescence intensity, high yield, simple preparation method and wide range of application.