The work aims to improve the mechanical properties and water resistance of cassava starch/polyvinyl al-cohol/chitosan composite films by adding nanomaterials and studying the nanomaterial dispersibility with cassava starch, polyvinyl alcohol and chitosan as the basic film-forming materials. Single factor experiments and orthogonal tests were carried out to investigate the effect of dispersibility of nanomaterials on the properties of cassava starch/polyvinyl alco-hol/chitosan films. The best dispersion conditions for nano-SiO2 were ultrasonic power of 240 W, ultrasonic temperature of 50 ℃, and ultrasonic time of 40 min. Under this condition, the composite film had a comprehensive score of 0.68. The ultrasonic temperature had the greatest effect on the properties of the composite film, followed by the time and power of the ultrasound, which improved the mechanical properties and water resistance of the composite film to some extent. The optimal dispersion conditions for nano-SiO2 are obtained when composite films are prepared, laying a foundation for the development of new composite film materials.