Abstract: In order to explore the effective purification technology for water soluble dietary fiber (SDF) from peanut hull, the suitable membrane module was determined. The separation of SDF extracting solution with ultrafiltration was conducted using membrane with different molecular weight cut-off and optimizing membrane separation process conditions. The results showed that PS-30 polysulfone membrane had the best separation effect under the operating conditions of pressure 0.08 MPa, ratio of material to liquid 1:75 g/mL, temperature 30℃. Under these conditions, the membrane flux reached 127.2 L/(m2·h), the yield of SDF was 67.56%, non-starch polysaccharides (NSP) quality fraction increased from 49.85% to 92.36%, and the protein quality fraction decreased from 5.53% to 0.92%. Compared with the conventional extraction method, ultrafiltration membrane separation technology has the advantages of short producing cycle, low manufacturing cost and high purity and quality.