Acorn starch was used as the main material.Thermoplastic acorn starch (TPAS) and binary composites of thermoplastic acorn starch(TPAS)/ Polycaprolactone (PCL) were prepared by hot-melt extrusion method.The effects of different plasticizers such as ethylene glycol, glycerol, monoethanolamine, iminobisetnanol and triethanolamine on molecular structure of samples were studied by FTIR and XRD analysis.In addition, the effects of different plasticizing system on molecular structure and mechanical properties of composites were also studied.The results showed that the addition of plasticizers changed the inter-molecular structure, and glycerol-based TPAS/PCL composites showed favorable mechanical properties.