Adding the plasticizing agent into starch, thermoplastics starchs was prepared. Plasticity of 3 kinds of starch and plasticizing effects of 4 kinds of plasticizing agent were studied. The property of the starch was different from each other according to different starch type and different plasticizer. Though the micro telescope, it can be seen that the secondary bonds were broken and starch crystal was destroyed after the starch was plasticized,thus endowing the starch thermoplasticity, and films can be processed with it.