Abstract: To explore the effects of different pretreatment methods on the structure and physicochemical properties of soluble dietary fiber (SDF) from millet bran and to achieve its high-value utilization. This study used millet bran as the raw material and SDF yield as the indicator. Single-factor and orthogonal experiments were employed to determine the optimal pretreatment conditions for the different pretreatment methods (ultrasound, superfine grinding, and ultrasound-superfine grinding combination). The effects of different treatment methods on the structure and physicochemical characteristics of millet bran SDF were analyzed by measuring indicators such as monosaccharide composition, molecular weight distribution, infrared spectra, internal particle structure, micro-morphology, thermogravimetric, water holding capacity, oil holding capacity, swelling capacity, and solubility. The results showed that under the conditions of grinding particle size of 800 mesh, solid-liquid ratio of 1:40 (g/mL), ultrasonic power of 330 W, and ultrasonic time of 50 min, the highest SDF yield of Millet Bran reached 20.44%±0.17%, representing a 2.68-fold increase in yield. Compared with conventional grinding, ultrasound, and superfine grinding, their combination altered the relative content of monosaccharide components in millet bran SDF. The combination of both methods increased the proportion of high molecular weight components to 45.42%, forming a loose and porous structure on the crystal surface, and had the most obvious effect on reducing its orderliness and thermal stability. Meanwhile, analysis of physicochemical characteristics indicated that the ultrasound-superfine grinding combination significantly improved the water-holding capacity, oil-holding capacity, swelling capacity, and solubility of millet bran SDF (P<0.05). Therefore, the combined treatment of ultrasound and superfine grinding enhances the physicochemical characteristics by improving its structure, thereby improving the processing performance and increasing the potential utilization value of millet bran SDF.