The invention relates to a Chinese medicinal feed additive for preventing and treating common diseases of chickens. The Chinese medicinal feed additive is prepared from the following selected raw materials according to parts by weight: radix scutellariae, rhizoma coptidis, golden cypress, milk veteh, fructus forsythiae, honeysuckle, rhizoma belamcandae, rhizoma atractylodis, fried bighead atractylodes rhizome, hawthorn, barley malt, medicated leaven, codonopsis pilosula and liquorice. A preparation method of the Chinese medicinal feed additive comprises the steps of mixing and then grinding the raw materials, or respectively grinding and then mixing the raw materials. The feed additive has the effects of strengthening body immunity to eliminate pathogenic factors, clearing away heat and toxic material, diminishing inflammation and invigorating stomach, sterilizing and disinfesting; by being mixed into daily feed for feeding, the Chinese medicinal feed additive can increase body immunity and disease resistance of chickens; and the feed additive is excellent in preventing and treating such common diseases of chickens as bird flu, new-area plague, salpingitis, white diarrhea, cholera,ascariasis, laryngotracheitis, coccidiosis and colon bacillus. Application proves that the Chinese medicinal feed additive has good preventing and treating effects, easily obtained materials, low cost and no toxic side effect.