Abstract: In order to solve the brittleness of conventional ethyl cellulose(EC) film, and improve its flexibility, 3 different sulfide polyols(EATP, ESTP, EHTP) were synthesized from soybean oil and its derivativesas, including epoxy fatty acid methyl ester, epoxy soybean oil. Next, these 3 polyols were physically blended with ethylcellulose(EC) at an experience weight ratio of 30∶70 to create 3 toughening modification composite EC-based films, and the properties were characterized by infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, scanning electron microscopy, thermogravimetric analysis, and dynamic mechanical thermal analysis. The results showed that the prepared 3 different soybean oil-based thioether polyols possessed good compatibility with EC, and there existed few holes on the fracture surface of prepared toughening modification EC composite films. Compared with EC film, the hydrophilicity and flexibility of the composite film were significantly enhanced, and the glass transition temperatures were also significantly reduced. Compared with EC film, the thermal stability of EATP and EHTP modified composite systems were slightly decreased, but ESTP modified composite system had more superior thermal stability than EC film.