The invention discloses a new microbial feed additive, a preparation method thereof, and the application in the animal and plant breeding. The feed additive is mainly composed of the following components with the parts by weight: 20 to 40 shares of Boas-Oppler bacillus, 20 to 40 shares of Saccharomyces cerevisiae, and 30 to 60 shares of Bacillus subtilis. The feed additive of the invention is rich in active ingredients including lactic acid, digestive ferment, amino acid, protein, vitamin, nutrilit, etc., and has the efficacy on the following aspects: 1. the autoimmunity of animals and poultries is improved, the disease rate of intestinal tract disease is reduced, and the mortality rate is lowered; 2. the production performance of the animals is improved; 3. the feed percent conversion is improved, the ratio of feed-meat, feed-egg, and the feed-milk is lowered; 4. the milk producing and egg-laying time of the animals and the poultries is prolonged, the outside and inside quality of the products of the animals and the poultries is improved, the content of cholesterol and fat is lowered, and the pesticide residue is deteriorated; 5. the odour of dejection of the animals and the poultries is eliminated, the shit and urine pollution in a breeding farm is lowered, the quantity of mosquito and fly is reduced, and the production condition is improved.