The invention discloses a preparation method of konjac glucomannan antibacterial sponge. The preparation method comprises the following steps: by means of a chemical reduction method and taking glucose as a reducer and polyvinylpyrrolidone as a dispersant, converting Ag ions in a silver nitrate solution in a weak alkaline heating condition into nanosilver; by taking konjac glucomannan as a raw material and sodium sulfate as a pore-foaming agent, generating a gel through a deacetylation reaction, and then obtaining konjac glucomannan sponge by means of a freeze-thaw method; and finally, performing action on konjac glucomannan sponge and nanosilver to prepare the konjac glucomannan antibacterial sponge. The method is simple in process, controllable in process, not high in equipment demand and low in energy consumption. The prepared konjac glucomannan antibacterial sponge is uniform in shape, compact in structure, high in water absorption, high in antibacterial property and easy to store.