The invention discloses a thionine-modified three-dimensional graphene material and a preparation method thereof. The preparation method includes the steps of firstly, dissolving thionine buffer solution 6.5-8.5 in pH to obtain thionine solution; and secondly, immersing three-dimensional graphene in thionine solution for modification to obtain the thionine-modified three-dimensional graphene material. Composition of thionine with three-dimensional graphene is achieved by means of simple non-covalent absorption, and the process is simple. The prepared thionine-modified three-dimensional graphene material is rich in macroporous and mesoporous structures, fine in electrical conductivity, and can be directly used as base electrodes without support loads.