With the rapid depletion of fossil fuels and a series of environmental problems, it is urgent to develop and to utilize new electrochemical energy storage devices, and the design, preparation and optimization of electrode materials are key factors to determine the performance of supercapacitors. Hydrothermal method was used to convert hollyhock stalks into porous carbon matrix with MnO and Co nanocrystals anchored on it. Results show that the prepared biocarbon has porous structure and good electron transport properties, and the nanosrystal MnO-Co on it has high capacitance. Due to the unique nanostructure of carbon skeleton and large specific surface area (345.9 m²·g^-1), MnO-Co nanocrystal/porous carbon shows excellent electrochemical capacitance (146 F·g^-1 at 1 A·g^-1) and cycle stability. After 1000 cycles, the specific capacity still remains 99.4%.