The invention relates to a graphene load flower manganese dioxide (MnO2) composite material and an ultrasonic synthetic method thereof. The graphene load flower MnO2 composite material is characterized in that flower MnO2 is composite with graphene layers, and the flower MnO2 is composed of a plurality of flakes which are mutually assembled. Graphene is used as a matrix skeleton and has favorable conductibility, and the flower MnO2 can have favorable conductibility through the graphene layers, thereby increasing the apparent conductivity of the composite material. The diameter of the flower MnO2 growing on both sides of the graphene is from 100 to 300 nm, and the thickness of each flake is from 1 to 10 nm. The material is prepared by the following two typical steps of preparing pyrolytic graphene and ultrasonically synthesizing the graphene load flower MnO2 composite material. The graphene load flower MnO2 composite material prepared by using the ultrasonic synthetic method has the advantages of simple process, high electrode capacitance and good cycle performance and is suitable for electrode materials of super capacitors.