China is the largest country of cultivating sweet potato in the world. The resources of sweet potato vines (SPV) are huge. To exploit the rich resources, SPV of XuShu 18 was selected as raw materials since it is cultivated in China widely. Polysaccharide from SPV was extracted by pilot instrument and precipitated by ethanol. The decolouring technology was studied. By primary purification, we obtained the polysaccharide from SPV (PSPV) and studied its physical and chemical characters. Using DEAE-cellulose column and NaCl solution as eluting reagent, three kinds of pure polysaccharide, named PSPV I, PSPV II and PSPVIII respectively, were obtained. Then the molecular weight distribution and sugar compositions were studied using High Performance Gel Filtration Chromatography and GC. The followings are the results. PSPV I was separated from PSPV which was extracted from SPV harvested in the middle of June. Its M.W. is 6.278 x 10(4) D and is mainly composed of Xylose, Mannose and Glucose. PSPV II and PSPVIII were separated from PSPV which was extracted from SPV harvested in the middle of October. Their M.W. are 3.801 x 10(4) D and 1.418 x 10(4) D respectively. PSPVII is mainly composed of mannose and galactan. PSPVIII is mainly composed of glucose, xylose and rhamnose. The results provide theoretical basis for the utilization of SPV.