The invention discloses a fermented feed additive, a preparation method and application thereof. The fermented feed additive is prepared by fermenting mixed strains and mixed auxiliary materials consisting of monosodium glutamate protein, bean pulp, bran, cottonseed meal, corn fibers, rice bran and powdered rice hulls, wherein the mixed strains are obtained by mixing activated strains of lactobacillus acidophilus, lactobacillus planetarium, lactobacillus casei, saccharomyces cerevisiae, bacillus subtilis and bacillus licheniformis in a proportion of (1-5): (1-5): (1-5): (1-5): (1-5): (1-5); and the dosage of the fermented feed additive is 5 to 100 percent of the weight of the animal feed when used for the animal feed. According to the fermented feed additive, the bean pulp, the bran, the cottonseed meal and other raw auxiliary materials are sufficiently utilized, so that the food consumption in the animal feeding process is reduced; the fermented feed additive can be used to partiallyor completely replace the animal feed, and antibiotic medicaments can be reduced or prevented from being used; and no medicament is left, so that the feeding cost of farmers is reduced.