Abstract: In order to improve the mechanical properties and water resistance of thermoplastic starch (TPS), the carboxylated silica microspheres (SM-COOH) modified by coupling agent KH550 and succinic anhydride were used to prepare the SM-COOH/TPS composites by extrusion and injection molding process. The effects of different contents of SM-COOH on the mechanical properties, dynamic thermodynamics, thermal stability, surface water resistance and rheological properties of the composites were studied in details. The results show that the added SM-COOH can improve the performance of TPS. When the content of SM-COOH is 2.0wt%, the tensile strength and impact strength of the composites reach the maximum value of 12.71 MPa and 15.918 kJ/m², respectively, which are nearly 4 times and 2.6 times higher than that of pure TPS. The temperature corresponding to the maximum decomposition rate in DTG curves reaches the maximum of 322.1℃, and the peak value and equilibrium torque of the composites are moderate, which shows the better rheological processing properties. In addition, with the increased SM-COOH content, the transition temperature and surface contact angle of composites also increase. Therefore, adding the carboxylated modified nano-SiO₂ into TPS is an effective method to improve the performance of SM-COOH/TPS composites, and will be useful in the area of starch-based biodegradable plastics.