The invention discloses a method for preparing fast dissolving selenium-rich rice flour by a wet granulating technology. The fast dissolving selenium-rich rice flour is prepared from the raw material of selenium-rich rice enriched by selenium biological nutrients through the technologies of soaking, pulping, wet granulating, quantitative subpackaging and the like. The granularity of the fast dissolving selenium-rich rice flour is 0.5-1 cm (long)*0.5-1cm (wide)*1-5mm (thick), the fast dissolving time is shorter than 20 seconds, and the selenium content is 5-30 micrograms every 100 grams of fast dissolving selenium-rich rice flour. The preparation of the fast dissolving rice flour is realized without adding. The product has fine taste and the fragrance of puffed rice, realizes selenium quantification and is particularly suitable for the selenium supplementing requirement of children.