In this paper,soluble dietary fiber from potato pulp was extracted by using L-ascorbic acid and sodium hexametaphosphate method.Its functional characteristics were also investigated,such as expansibility,retention ability,water solubility.The optimization processing were studied by the comparison of the ratio of solution and the dregs,the concentration of sodium hexametaphosphate(SHMP),promoter L-ascorbic acid,the extraction temperature and time,the ratio of ethanol volume(the filtrate to liquid).The optimum extraction conditions were: mixed with 0.5% sodium hexametaphosphate solution and 75 mg of L-ascorbic acid as promoter at the ratio of 30:1.The mixture was kept at 95℃ for 2.5h,and the ratio of ethanol volume(the filtrate to liquid) was 1:1.The soluble dietary fiber was thus extracted with the yield of 43.4%.The soluble dietary fiber from potato pulp had good water solubility(56.15%),expansibility(7.72 g/g) and retention ability(7.56 mL/g) in pH 7 at 37℃.