The invention discloses a polysaccharide from Eucommia ulmoides leaves with anti-complement activity, and its method of extracting, separating and purifying, wherein, the polysaccharide from Eucommia ulmoides leaves with anti-complement activity is an acidic polysaccharide. The extraction method comprises the following steps: adding eucommia fragments in petroleum ether, reflowing and magnetic stirring, and extracting filtration; air drying the residues, then using hot water for boiling-refluxing extraction, filtering and removing the residues with gauze; extracting the extract, carrying out decompression condense; mixing the polysaccharide concentrate with waterless ethanol, standing for precipitation, and using centrifugation to obtain a alcohol precipitated polysaccharide. The separating and purifying method comprises the following steps: producing a polysaccharide solution from crude polysaccharide, extracting filtration, and using macroporous resin to decolour; removing protein by using Sevag method, mixing Sevag reagent with the polysaccharide sample uniformly, carrying out centrifugation, collecting supernatant and condensing, UV-scanning until no absorption peak; respectively dialyzing the crude polysaccharide solution; weighing polysaccharide to dissolve in distilled water, and eluting on a cellulose column to obtain the monomer component of refined polysaccharide. The method realizes the exploitation of folium cortex eucommiae resource, lays a foundation for the application in pharmacy industry, and serves the health of human.