The invention discloses a method for preparing champignon polypeptide powder, which comprises the following steps of: crushing mushroom fruit bodies, taking mushroom fruit body powder, and mixing the mushroom fruit body powder with water; adding cellulase into the mixture to perform enzymolysis for 1 to 2 hours, and then adding protease into the mixture to perform enzymolysis for 3 to 6 hours; and inactivating the enzymes, concentrating an enzymolysis solution, adding a flavoring agent into the enzymolysis solution, and embedding and drying the mixture to obtain a product. The product prepared by the method has high amino acid content, rich nutrients and high freshness, and not only can be applied to conditioning essence reactive perfume bases, but also can be applied to the industries of bio-pharmaceuticals, nutritional health products, domestic flavoring materials, instant noodle seasonings, puffed foods, bakery foods, meat processed products and the like; besides, the method has the advantages of high utilization rate of mushrooms, less waste and low production cost, is suitable for processing a large amount of products, and is a good method for the deep processing of the mushrooms.