Chemical fabrication of a nanocomposite structure for electrode materials to regulate the ion diffusion channels and charge transfer resistances and Faradaic active sites is a versatile strategy towards building a high-performance supercapacitor. Here, a new ternary flower-sphere-like nanocomposite MnO2-graphite (MG)/reduced graphene oxide (RGO) was designed using the RGO as a coating for the MG. MnO2-graphite (MnO2-4) was obtained by KMnO4 oxidizing the pretreated graphite in an acidic medium (pH = 4). The GO coating was finally reduced by the NaBH4 to prepare the ternary nanocomposite MG. The microstructures and pore sizes were investigated by x-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and nitrogen adsorption/desorption. The electrochemical properties of MG were systematically investigated by the cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy in Na2SO4 solution. The MG as an electrode material for supercapacitor exhibits a specific capacitance of 478.2 and 454.6 F g-1 at a current density of 1.0 and 10.0 A g-1, respectively. In addition, the capacitance retention was 90% after 8,000 cycles. The ternary nanocomposite enhanced electrochemical performance originates from the specific flower-sphere-like morphology and coating architecture bringing higher specific surface area and lower charge transfer resistance (Rct).