The research on the extraction of polysaccharides from stem of sweet potato cultivar LUSHU NO.7 by orthogonal designs is described in this paper.The suitable conditions was adding 30 times of water,keeping at 100℃ For 25 minute.By means of brown-ring test,anthrone-surfuric ama colorimetric methods,Fehling's test and Biuret reaction,the final extracted substance from the stem of sweet potato is identified as polysaccharide.The polysaccharides from growing-stem,matured-stem and stem at harvesting period,and r...