Micronized starch (MST) was prepared by using supersonic blast air current pulverizer, and the optimized plasticization condition of micronized starch was confirmed. At the same time, the structure and properties of thermoplastic micronized starch were characterized by using scanning electron microscopy, mechanical test and differential scanning calorimetry. The best plasticization condition of micronized starch was: glycerol/PVA(Polyvinyl Alcohol)(V/V)=5∶1, 80% MST, blending temperature 160℃ and screw speed 40 r/min. Scanning electron microscopy(SEM) photograph showed that the surface of thermoplastic micronized starch sheet was smooth and its tensile strength and breaking elongation are 17.36 MPa and 138.29% respectively. Differential scanning calorimetry(DSC) curve indicated that thermoplastic micronized starch melt at 130～155℃ and its mechanic properties were excellent.