The invention discloses an efficient extraction method of selenium-enriched mushroom powder selenium polysaccharide, which comprises the following steps: mixing selenium-rich mushroom powder with ethanol, refluxing, carrying out suction filtration, and carrying out vacuum drying to obtain degreased mushroom powder; mixing the dried degreased mushroom powder with distilled water, adjusting the pH value, adding cellulase, carrying out ultrasonic enzymolysis, heating for enzyme deactivation, carrying out high-temperature digestion, and centrifuging to obtain an extract liquid; carrying out rotaryevaporation concentration, alcohol precipitation and centrifugation on the extract liquid to obtain precipitate, and carrying out vacuum drying to obtain crude selenium polysaccharide; and redissolving the crude selenium polysaccharide with distilled water, adding neutral protease for enzymolysis, centrifuging, removing protein from the supernatant with a Sevage reagent, centrifuging, dialyzing,and freeze-drying to obtain the mushroom powder selenium polysaccharide. According to the method, the selenium polysaccharide is extracted by adopting an ultrasonic synergistic cellulase method assisted by high-temperature digestion, so that the extraction rate of the selenium polysaccharide is greatly improved; protease-Sevage reagent combined protein removal is adopted, the protein removal effect is good, and selenium polysaccharide loss is small. The extraction method is simple and feasible, the extraction rate of the selenium polysaccharide is high, impurities are few, and the method has good application value and market potential.