The invention relates to a premixed feed for preventing Mycoplasma gallisepricum, and a preparation method thereof. The premixed feed comprises, by weight, 5-7 parts of Radix Scutellariae, 4-6 parts of Amur Corktree Bark, 6-10 parts of Rhizoma Dioscoreae Bulbiferae, 6-10 parts of honeysuckle flower, 6-10 parts of Fructus Gardeniae, 4-6 parts of radix bupleuri, 25-35 parts of Folium Isatidis, 6-10 parts of Divaricate Saposhnikovia Root, 4-6 parts of realgar, 4-6 parts of alum, 8-12 parts of licorice root, and 1-3 parts of vitamin C. The premixed feed is composed of above traditional Chinese medicines, and can well prevent and treat the Mycoplasma gallisepricum. The performances of the premixed feed are better than effects of antibiotics on chickens. The performances of Chinese herbal medicines in the above composition make Mycoplasma gallisepticum viruses be outward drained from the chickens through defecation channels. The premixed feed also allows young protomers in the invisible stage of chickens to be killed and then to be drained through the defecation channels in order to eliminate hidden Mycoplasma gallisepricum troubles. The premixed feed adapts to all fertility stages of fryers, and has no residual and no toxic or side effects on the chickens.