Nano-TiO2 dispersed by ultrasonic wave was added into soy protein/polyvinyl alcohol composite film on a glass plate through casting technique. Effects of particle size, mass fraction of nano-TiO2 and the type of dispersant composite films were studied based on the evaluation index of tensile strength, breaking elongation, transmittance and water absorption of the films. Experimental results showed that in the performance optimization of soy protein / PVA composite film, the nano-TiO2 particle size, mass fraction and the type of dispersant exerted certain effects. When the Nano-TiO2 particle size was 30 nm, the mass fraction was 1.50%, dispersant was PVPK-30, the best performance was achieved. Compared with the film with no nano-TiO2, tensile strength of the composite film increased to 5.4 MPa from 4.6 MPa while breaking elongation rate increased to 87.4% from 56.3%, transmittance rate increased to 28.9% from 13.7% , and water absorption decreased from 48.7% to 36.3%.