The invention discloses a Chinese cordyceps sinensis protein polysaccharide and preparation and application thereof. The Chinese cordyceps sinensis protein polysaccharide is composed of polysaccharide with 55%-60% weight percentage and protein with 40%-45% weight percentage; and the ingredients of the polysaccharide are mannose, ribose, glucose, galactose, xylose and arabinose; the ratio of amount of substances among the mannose, the ribose, the glucose, the galactose, the xylose and the arabinose is 6.42-6.51: 2.20-2.32: 65.85-65.95: 2.10-2.18: 4.20-4.30. The Chinese cordyceps sinensis protein polysaccharide preparation method comprises the following steps: extracting the Chinese cordyceps sinensis protein polysaccharide by aqueous extract and alcohol precipitation, removing the protein, dialyzing, exchanging chromatography by anion and purifying gel filter layer chromatography through an enzyme-Sevage combination method, and freezing, drying and separating purification components in vacuum, and the Chinese cordyceps sinensis protein polysaccharide is acquired. According to the preparation and the application thereof, proximate analysis, structural identification and immunologic function study are carried out on the components of polysaccharide after purification, and the facts that the Chinese cordyceps sinensis protein polysaccharide has strong immunoregulation activity and is a potential immunological enhancement substance are discovered.