Corn straw cellulose triacetate (CTA) was used as raw material. Self-made ionic liquid phosphotungstate [PyPS]3PW12O40 (ILP) was used as hydrolysis catalyst. A green and efficient process for the preparation of cellulose diacetate (CDA) was proposed. Taking the degree of substitution and mass fraction of CDA as evaluation indexes, the effects of water addition, ILP addition and reaction time on the degree of substitution and mass fraction of hydrolysate were analyzed, and the physicochemical properties and structure of the products were characterized. The results showed that when CTA was 0.6g and reaction temperature was 110℃, the optimal hydrolysis conditions of CDA were as follows: water addition was 0.3g and ILP addition was 0.1g, that was, the mass ratio of ILP to water in hydrolysate was 1∶3, the mass ratio of raw materials to hydrolysate was 3∶2, and the reaction time was 60min. The degree of substitution of CDA was 2.62 and the mass fraction was 69.33%. The degree of polymerization CDA was 66.54, which can be dissolved in acetone, glacial acetic acid, dichloromethane, 1,4-dioxane and dimethyl sulfoxide. The physical and chemical properties of the product were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analysis.The results of scanning electron microscope (SEM) showed that the microstructure of CDA was rough and scattered, and the surface damage was serious. Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis showed that CTA was successfully hydrolyzed into CDA. The research can provide an idea for the preparation process of CDA. When corn straw was used as raw material, the mass conversion rate of raw material reached 47.72%, which was of great significance to the diversified utilization of corn straw.