The invention provides a preparation method of a feed additive. The feed additive comprises the following components of, in parts by weight, 0.1-5 parts of probiotics, 10-20 parts of beer yeast powder, 20-70 parts of fermented feed raw materials, 10-60 parts of vegetable oil, 5-20 parts of lecithin and 5-20 parts of sucrose ester. The preparation method of the feed additive comprises the followingsteps of emulsifying the vegetable oil, mixing with the powder and the like. According to the preparation method, the feed additive is scientific and reasonable in formula composition, rich in emulsified fat, fermented protein and compound polysaccharide, high in nutrition degree, rich in fragrance, capable of promoting ingestion and increasing daily gain of animals, easy to absorb, capable of improving the intestinal microecological environment, capable of reducing digestive tract diseases and capable of reducing the diarrhea rate and the death and culling rate; the animal reproductive performance is improved, lactation is improved, and the estrus interval is shortened; the laying rate of laying hens, eggshell quality and breeding hen semen quality are improved; and biological raw materials such as fish meal, emulsified fat powder, plasma protein, glucose and fermented soybean meal in the feed can be partially replaced, and the feed conversion rate is increased.