The invention relates to hydrothermal carbon spheres for supporting nanosilver by using a one-step method and a preparation method and application of the hydrothermal carbon spheres. The preparation method comprises the following steps: removing impurities from whole collected biomass components, washing, drying, preparing fine granules under the external mechanical actions of a crushing machine and a ball mill, dissolving the whole biomass components into a sodium hydroxide/urea system, after the solution is dissolved, dropping a prepared silver ammonia solution, uniformly mixing, pouring theuniformly mixed solution into a high-temperature high-pressure reaction kettle, carrying out a hydrothermal reaction, and after the hydrothermal reaction is completed, carrying out centrifugation, washing, ultrasonic treatment, centrifugation and freeze drying on the solution, thereby obtaining the nanosilver supported hydrothermal carbon spheres finally. By adopting the hydrothermal carbon spheres, the defects that nanosilver is liable to aggregate, instable and too rapid in leakage can be alleviated, the application range of the hydrothermal carbon spheres as a nanosilver carrier is widened, and whole biomass components such as agriculture and forestry biomass wastes can be sufficiently utilized.