The invention discloses a method for preparing additive-free instant selenium-enriched corn flour by a spray-drying process. The method is characterized by comprising the following steps: with selenium-enriched corns subjected to selenium biological nutrient enrichment as a raw material, performing processes of cleaning, peeling, degerming, powder coarsening, curing, powder thinning, slurry settling, spray drying, and quantitative subpackaging to prepare the additive-free instant selenium-enriched corn flour with the water content of less than 7wt%, the granularity of 100-120 meshes, the instant time of shorter than 30 seconds and the selenium content of 10-250 micrograms / 10 grams. The method disclosed by the invention realizes preparation of the instant corn flour under an additive-free condition; the instant corn flour is fine and smooth in taste, has the fragrance of puffed corn flour, realizes selenium quantification, and provides a proper and scientific choice for different people with the need of selenium supplement.