The invention discloses a method for producing fee through biological fermentation of distiller's grains. The method comprises the following producing processes: 1. preparing and mixing materials, namely, dissolving an enzyme preparation and inorganic nitrogen which are externally added in water, and directly mixing uniformly with distiller's grains; 2. inoculating, wherein strain is mainly derived from animal probiotic microorganisms, and includes, but not limited in, brewer's yeast, candida utilis, endomycopsis fibuligera, bacillus subtilis, bacillus licheniformis, trichoderma koningii, geotrichum candidum and the like; 3. large-scale fermentation, namely, implementing single-bacterium or multi-bacteria mixed fermentation through a fermentation box; 4. drying; 5. rice husk separation, namely, beating dried product for several times, oscillating and filtering through a 40-60-mesh sieve to remove most rice husks; and 6. grinding and packaging. The feed disclosed by the invention is rich in mycoprotein, vitamins and bioactive substances, crude protein content is no less than 25%, and amino acid composition is rich and complete; furthermore, the product is abundant in probiotics and free from foreign sell of fresh distiller's grains, and is relatively high in feeding value. The method disclosed by the invention is short in fermentation cycle, high in automation degree and production efficiency and low in production cost, and provides a good industrial way for comprehensive treatment of distiller's grains on a large scale.