The invention discloses a biodegradation composition, and a preparation method and application thereof. The biodegradation composition consists of a biodegradation resin, dextrin and a plasticizer, wherein the mass ratio of the biodegradation resin to the dextrin is 1:9 to 9:1; the content of the plasticizer is 1 to 30 percent based on the total weight of the biodegradation composition; and the dextrin is prepared from the mixture of dried natural starch and acid solution in melting and mixing equipment. The biodegradation composition is prepared from the mixture of the components in the smelting and mixing equipment. The biodegradation composition provided by the invention has relatively higher physical properties and processability, relatively higher water resistance and medium biodegradation speed, well satisfies the needs of practical application, and can be prepared into various products by universal processing methods such as blowing molding, extrusion molding, injection molding, spinning molding and the like.