Octenyl succinic anhydride modified starch is an important esterifying agent, but its film-forming property needs to be improved. In this paper, taking the enzymatic hydrolysis of octenyl succinic anhydride modified waxy corn starch (OSS) as raw material, trisodium trimetaphosphate as modifier, the modified OSS films were prepared. The modified conditions were optimized by single-factor and response surface experiments using the tensile strength of films as the response value, and the structure of modified OSS films obtained under the optimal conditions was characterized. The results showed that the optimal process conditions were: 5.8 h for reaction time, 6.8 for reaction pH value, 18.0% for trisodium trimetaphosphate addition, and the tensile strength of modified OSS films obtained under these conditions was 2.19 MPa, 69.77% higher than the contrast. After modification, the cross section of OSS films were relatively homogeneous, and the onset phase transition temperature increased 14.6 ℃. The results of 31PNMR and FTIR showed that trisodium trimetaphosphate and OSS were associated to improve the performance of OSS films in the form of hydrogen bond. It is found that the film-forming property and the storage stability in high temperature of emulsive films could be effectively improved by modification of trisodium trimetaphosphate after emulsification of OSS with Vitamin E.