The invention provides a selenium-enriched five-cereal nutritional instant powder and a preparation method thereof, not only realizes the preparation of instant composite coarse cereal powder under the no addition condition, and has the advantages that the product taste is fine, has the fragrance of puffing coarse cereals, the selenium quantification can be realized, and the product is suitable for demands for selenium supplementation of crowds with selenium deficiency. The five-cereal nutritional instant powder rich in selenium comprises selenium-enriched rice and various cereals as well as auxiliary materials, can be selenium-containing hair nourishing brain strengthening nutrient powder, selenium-containing children's nutrient powder, selenium-containing blood and qi nourishing nutrient powder or selenium-enriched liver nourishing and protecting nutrient powder. The preparation method comprises the steps of soaking fresh five cereals taken as raw materials, mixing the soaked five cereals and water, drying and smashing to obtain five-cereal powder; mixing the five-cereal powder and ethyl alcohol to prepare soft material, then carrying out granulation to obtain five-cereal instant particles; and drying the five-cereal instant particles to obtain the five-cereal instant powder. The preparation method for the five-cereal nutritional instant powder is simple, the obtained five-cereal instant powder is easy to dissolve, the instant time is less than 20 seconds, and the agglomeration probability is low.