The invention discloses a feed additive for reducing stress of sows and a preparation method thereof. The additive is prepared from the following components in parts by weight: 6 to 15 parts of folium isatidis, 1 to 5 parts of chrysanthemum, 2 to 12 parts of honeysuckle flower, 6 to 20 parts of houttuynia cordata, 8 to 20 parts of isatis root, 8 to 20 parts of radix bupleuri, 5 to 15 parts of scutellaria baicalensis, 5 to 10 parts of hawthorn, 3 to 12 parts of liquorice, 5 to 15 parts of astragalus membranaceus, 2 to 12 parts of golden cypress, 3 to 15 parts of schizonepeta, 2 to 12 parts of cyrtomium fortune, 4 to 16 parts of fructus forsythia, 4 to 16 parts of elephantopus tomentosus, 10 to 20 parts of gypsum, 2 to 12 parts of coptis chinensis, 3 to 15 parts of fructus gardenia, 5 to 10 parts of endothelium corneum gigeriae galli, 5 to 10 parts of medical stone, 1 to 5 parts of candida utilis powder, 1 to 5 parts of bacillus subtilis powder, 1 to 5 parts of enterococcus faecalis powder, 0.5 to 1 part of folic acid, and 0.5 to 1 part of vitamin C. According to the feed additive, the components are mixed to achieve high capacity of strengthening the spleen and harmonizing the stomach, removing food retention and stagnancy, clearing away heat and toxic materials, eliminating dampness and de-worming, resisting viruses, diminishing inflammation, maintaining normal functions of the reproductive system, and improving the body resistance to diseases and stress resistance; the probability of reduction of production performance of the sows caused by stress, in particular thermal stress, can be greatly reduced.