Abstract: With the same ultrasonic time and temperature, different ultrasonic powers of 0, 25, 50, 100, 150, 200, 250 W on the structure and properties of millet starch were studied. The hydrolysis rate, microstructure, crystal structure, molecular structure, particle size, rheological and gelatinization properties of millet starch were determined. The experimental results indicated that the hydrolysis rate and particle size of millet starch increased after ultrasonic treatment, hydrolysis rate of millet starch under 250 W ultrasonic treatment for 40 min was 1.037%, the average particle size increased from the original 9.96 to 12.10 μm, and it showed greater transparency and stability. Ultrasonic treatment did not change the crystal type and molecular structure, but caused a slight decrease in order. Ultrasound changed the fluidity of millet starch paste, the shear stress and apparent viscosity of millet starch paste decreased with the increase of ultrasonic power. The peak viscosity, trough viscosity, final viscosity, breakdown and setback of millet starch after ultrasound were significantly reduced, and the thermal stability was improved. Ultrasonic technology would be widely used in the processing of modified starch. The results of this study could provide a theoretical basis for the modification of millet starch.