The invention provides a wall breaking agent for sludge and a preparation method of the wall breaking agent. The wall breaking agent is prepared by compounding a targeting agent, a bactericide, a penetrating agent and a cross-linking agent in sequence and proportion. According to the provided hydrophobic skeleton and preparation method, biomass powder or treated modified dry sludge is used as a filler base material, and the wall breaking agent is dried and loaded on the filler base material to be mixed and prepared. The invention also provides a sludge reduction method for a sewage plant, which comprises the following steps: increasing the solid content of water-containing sludge to 4-5%, adding the wall breaking agent, adding a hydrophobic skeleton, uniformly stirring them, carrying out areaction process, carrying out pressure filtration dehydration on the obtained mixed liquid to obtain sludge cake with the water content of 45-48%, carrying out mud cake recovery, outward transport landfill or incineration, or selection of a part of sludge as a filler base material in the hydrophobic skeleton, and recycling a filter pressing liquid as a carbon source for a sewage treatment system. According to the method, the floc structure of the sludge can be fully destroyed, the water content of the dewatered water-containing sludge is reduced with low energy consumption and cost, microorganisms can be killed, odor can be removed, toxic substances in the sludge can be adsorbed, and treated solids and liquid can be recycled.