The invention relates to a lactation promoting soup and a preparation method thereof, belonging to the field of traditional Chinese medicines. The lactation promoting soup is suitable for puerperae little in milk secretion and dilute in milk, and is prepared from the following raw medicines in parts by weight: 7-10 parts of Chinese date, 10-15 parts of angelica sinensis, 6-9 parts of cowherb seed, 4-6 parts of parched pangolin scales, 4-6 parts of ricepaperplant pith, 5-7 parts of beautiful sweetgum fruit, 5-7 parts of uniflower swisscentaury root, 14-18 parts of prepared rehmannia root, 15-20 parts of raw astragalus and 14-18 parts of radix codonopsis. The preparation method comprises the steps of: proportionally weighing the raw medicines, then putting the medicines in a ware together, adding water 15 times the mass of the materials, soaking for 20min, boiling with big fire, decocting for half an hour with small fire, removing residues, and taking out the soup. The taking method is as follows: twice a day, 400ml every time and continuously taking for 3-5 days. The lactation promoting soup has the effects of invigorating Qi and blood, strengthening the spleen and stomach, regulating yin and yang, nourishing blood and yin, tonifying lactogenesis, and is capable of achieving an ideal lactation promoting effect in a shorter time.