The invention relates to an animal feed and a preparation method thereof. The animal feed is prepared from the following raw materials: 40 parts of codonopsis pilosula, 40 parts of dried tangerine peels, 30 parts of milkvetch roots, 30 parts of Chinese angelica, 30 parts of medicated leaven, 20 parts of red halloysite, 30 parts of areca seeds, 20 parts of sulfur, 20 parts of Chinese ephedra, 20 parts of alumen, 20 parts of hawthorn fruits, 150 parts of cereal flour, 120 parts of meat and bone meal and 4 parts of edible salt. The preparation method of the animal feed comprises the following steps of: smashing the Chinese medicinal herbs, sieving the powder with a 60-mesh sieve, mixing the powder of the Chinese medicinal herbs, adding the cereal flour, meat and bone meal and edible salt into the powder of the Chinese medicinal herbs and stirring uniformly, and filling the mixture into a bag to obtain a finished product. The animal feed provided by the invention can be used for preventing and treating common pathogenic bacteria and infectious viruses of the livestock and the poultry.