In order to improve the mechanical and water resistance of thermoplastic starch (TPS), The effects of PR (Polymerized Rosin) and glycerol on the molecular structure, mechanics, cross-section morphology, thermal properties and water resistance of TPS were investigated by FTIR, electronic universal testing machine, scanning electron microscopy, thermogravimetric analyzer and contact angle tester. The results showed that the carboxyl group in PR was esterified with the OH on TPS, and with the increased content of PR , the tensile strength, bending strength and thermal properties of the sample gradually increased, while the elongation at break, impact strength and moisture absorption rate gradually decreased. When the mass fraction of PR was 10% and the mass fraction of glycerol was 15%, 80PR-TPS had the best properties, and its tensile and bending strengths reached the maximum of 15.25 MPa and 25.83 MPa, respectively, which were 8.81 and 23 times of TPS, while the elongation at break and impact strength decreased significantly. The contact angle reached the maximum78.8°, which is nearly 2.9 times that of TPS, and the equilibrium moisture absorption rate decreased from 9.60% of TPS to 6.37%, indicating improved water resistance. In addition, the thermal performance is also significantly improved.