Thermoplastic starch was prepared with cross-linked hydroxypropyl starch by double screw extruder,glycerol was used as plasticizer.The factors that affected extrusion swell of thermoplastic starch were optimized by response surface based on the single factor experiment.The results showed that the best condition was : glycerol 30.7%,extruder temperatures 136.6℃ and rotational frequency 16.4Hz.under the above conditions,the expansion ration was 172.4%.Meanwhile,the thermoplastic starch was used in blowing models.After being stored for 24h at RH=50%,the tensile strength and elongation of TPS reached to 10.1 MPa and 107.4% respectively.