The present invention is epimedium polysaccharide and its application in preparing medicine for raising body's immunity. The epimedium polysaccharide consists of two parts, A and B and includes sevenmonosaccharides: rhamnose, fucose, arabinose, xylose, mannose, glycose and galactose. It has obvious immunity promoting effect and is one kind of biological regulator with excellent development future and may be used in auxiliary treatment of breast cancer, small-cell carcinoma of the lung, non-Hodgkin's lymphoid disease, etc.