In this work, the ultrasound was applied to oxidation of cassava starch, and the properties of the oxidized starch were studied，moreover, the properties of oxidized starch with and without ultrasound, and natural cassava starch (NCS) were compared. The results show that, compared to NCS，the solubility, transparency and whiteness of oxidized starch increased by 4.55 times, 3.38 times and 1.23% respectively, and retrogradation and gelatinization enthalpy value decreased by 99.05% and 45.79%, oxidized starch prepared by above two treatments had good capacity of forming film,its film was uniform and resilient, but the NCS was very difficult to form film. Under the same conditions, the properties of oxidized starch could be improved by ultrasound significantly, the solubility, transparency of the oxidized starch under ultrasound were increased by 97.23%, 33.68% respectively, whiteness had a 0.26% improvement（they had significant difference at 5% level）,the retrogradation and gelatinization enthalpy value were reduced by 78.80% and 24.13%. So, ultrasound can applied to effectively modify cassava starch.