The present invention relates to selenium-enriched rhizoma polygonati full powder and a preparation method thereof. The selenium-enriched rhizoma polygonati full powder contains 60-80% of rhizoma polygonati and 20-40% of maltodextrin. A processing method of the selenium-enriched rhizoma polygonati full powder is as follows: the selenium-enriched rhizoma polygonati in selenium-enriched production places is washed and impurities are removed, the impurity removed rhizoma polygonati is soaked by using a rhizoma polygonati peeling agent, and the soaked rhizoma polygonati is peeled by using nylon rolling brushers; after the peeling, citric acid solution is used to wash and neutralize surface residual alkaline liquor; the peeled selenium enriched rhizoma polygonati is subjected to treatment at a high temperature of 105-115 DEG C and under a high pressure for 90-180 min; the processed selenium-enriched rhizoma polygonati is beat into slurry and then the slurry is subjected to high-temperature saccharifying enzyme enzymolysis; a certain amount of a drying aid (the maltodextrin) is added into the enzymolyzed selenium-rich rhizoma polygonati homogenate, and the mixture is homogenized by using a colloid mill; and after the homogenization, the rhizoma polygonati homogenate is subjected to spray drying to obtain the selenium-enriched rhizoma polygonati full powder. The obtained products are light yellow powdery solid, have a certain water solubility, are rich in organic selenium, rhizoma polygonati polysaccharides and other functional ingredients, and have the characteristics of being simple in consumption, high in functional ingredient content, etc., and the preparation method is simple in technology, convenient in operation and relatively low in costs.