In this experiment， soluble dietary fiber (SDF) was extracted from millet by enzymatic method. The oil holding capacity， solubility and adsorption of cholesterol and NO₂- of SDF were determined， and the monosaccharide composition and molecular weight of SDF were studied. At the same time， the effects of SDF on the growth of Lactobacillus plantarum， Lactobacillus rhamnosus， Lactobacillus fermentans， Lactobacillus acidophilus， Bifidobacterium brevis， Escherichia coli and Staphylococcus aureus were analyzed. The results showed that the oil holding capacity and solubility of SDF were 4.05 g/g and 1.78 g/100mL. When pH was 2.0， the adsorption capacity of SDF for cholesterol and NO₂- was 16.22 μg/g and 6.97 μg/g respectively. At pH 7.0， the adsorption capacity of SDF for cholesterol and NO₂- was 26.31 μg/g and 2.77 μg/g respectively. Infrared spectrum analysis showed that SDF had typical polysaccharide characteristics. Chromatography showed that SDF was a heteropolysaccharide with a molecular weight of 1 784 u. SDF was composed of fucose， arabinose， galactose， glucose， mannose and glucuronic acid with a molar ratio of 0.02 ∶ 0.27 ∶ 0.26 ∶ 98.34 ∶ 0.95 ∶0.15， respectively. In the range of 5~20 mg/mL， SDF showed significant promoting effects on Lactobacillus plantarum， Lactobacillus rhanosus， Lactobacillus fermentans， Lactobacillus acidophilus， and Bifidobacterium brevis， and showed significant inhibitory effects on Escherichia coli and Staphylococcus aureus in a concentration dependent manner. In addition， SDF added to the medium significantly reduced pH compared to the control， which was conducive to the growth and reproduction of beneficial microorganisms in the gut. The results of this experiment can provide a theoretical basis for further study of SDF and development and utilization of millet resources.