The invention relates to a Chinese angelica acidic polysaccharide component, a preparation method thereof, and an application thereof in the preparation of drugs and health products for preventing cancers, enhancing immunity and preventing radiation damages, and belongs to the field of traditional Chinese medicine modernization. The method comprises the following steps: degreasing Chinese angelica roots, carrying out refluxing extraction with alkaline water, precipitating polysaccharides with alcohol, removing proteins, carrying out dialysis, carrying out anion exchange column DEAE serial column grading, eluting a part size exclusion chromatograph with 0.5mol/L of NaCl, further purifying, carrying out reduced pressure concentration on the above obtained 50kD or above component, and freeze-drying the obtained concentrate to obtain the Chinese angelica acidic polysaccharide component. The Chinese angelica acidic polysaccharide component has substantial cancer prevention, immunity enhancement and radiation damage prevention effects.