The invention relates to a novel highly effective chlorinated paraffin stabilizer, which is specifically prepared from 70 to 75 parts of modified branched epoxy resin with a special structure, 5 to 15parts of metallic soap, 10 to 17 parts of phosphite ester and 5 to 8 parts of co-stabilizer, wherein the modified branched epoxy resin with the special structure has a large number of alkyl epoxy groups, playing an important role in increasing the stability of chlorinated paraffin. Compared with the prior art, the novel highly effective chlorinated paraffin stabilizer has the advantages of good effect in increasing the thermal stability of chlorinated paraffin, outstanding plasticizing property and lubricating property, low price, environment-friendliness and the like, and has a broad application prospect.