The invention discloses an anion feed additive for cows. The anion feed additive is prepared from the following raw materials in parts by weight: 18 parts of ammonium chloride, 20 parts of magnesium sulphate, 7 parts of magnesium chloride, 4 parts of calcium sulphate, 26 parts of bran, 17 parts of corn and 8 parts of starch. The invention further provides a preparation method and application of the anion feed additive. The anion feed additive for the cows as well as the preparation method and the application of the anion feed additive, which are disclosed by the invention, have the benefits that the PH value of urine and the contents of Ca2+, P3- and Mg2+ in serum of a multiparous cow can be effectively regulated, so that postpartum paralysis of the cow is prevented; the anion additive is added 2-3 weeks before parturition of the multiparous cow, so that the postpartum paralysis and secondary diseases of retained placenta, the postpartum paralysis, metritis and the like can be effectively prevented; hybridization of the cow is easy, and the conception rate during sexual period is high; besides lactation peak is early, the recovery of a womb is facilitated, and the reproductive property of the cow is improved; besides the price is lower than that of a conventional product on sell, so that medical cost and human resources are reduced, and the healthy development of dairy industry is facilitated.