The invention relates to a preparation method of a medicine for treating infantile eczema. The method comprises the following steps: weighing raw materials of 90 g of tendon strengthening grass, 80 g of thin evodia, 80 g of Siberian alder bark, 80 g of common sage herb, 70 g of adoniside, 70 g of viola arcuata, 70 g of semen cassiae, 60 g of conical silene herb, 60 g of laciniate blumea herb, 60 g of chien briggsia herb, 50 g of narrowleaf burmann cinnamon roots and leaves, 50 g of radish seed, 50 g of pectinate rungia herb, 50 g of soroseris gillii, 50 g of anderson cirrhopetalum herb, 40 g of ainsliaefolious cacalia roots, 40 g of erigeron canadensis l., 30 g of hydrocotyle sibthorpioides, 30 g of hairyfruit musella flowers and 20 g of licorice roots. The preparation method comprises the following steps: adding 8000 ml of water, heating the weighed raw materials and the water for 5 hours under a reflux condition, and performing filtration so as to obtain a filter residue 1 and a filtrate 1; adding 6000 ml of water to the filter residue 1, heating the filter residue 1 and the water for 3 hours under the reflux condition, and performing filtration so as to obtain a filter residue 2 and a filtrate 2; merging the filtrate 1 and the filtrate 2 so as to obtain the medicine. The preparation method disclosed by the invention combines various medicines, and the formula is reasonable. According to the preparation method disclosed by the invention, various medicines are combined and used, manifestation and root causes are considered, and the medicine prepared by the method has the characteristics of precise curative effects, high security, high convenience, zero toxic or side effects, and low cost.