The invention relates to a preparation method of an acidulant special for feeds. The preparation method comprises the following steps of A, performing mixing and stirring; B, performing a condensation reaction on lactic acid to form polylactic acid; C, regulating the PH value with acetic acid; D, performing adsorption and bonding; and E, performing compression, drying and disinfection. According to the preparation method disclosed by the invention, the materials are easy to obtain, the preparation method is simple, the cost is low, the PH value of the gastrointestinal tract is reduced, the enzymic activity of the alimentary tract and the digestibility of nutrient substances are improved, the structure of microorganism microbial population is regulated, the acidulant participates in metabolism in organisms, absorption is more facilitated, the immunity is enhanced, stress is alleviated, the palatability is improved, the food consumption is increased, the regulation is stable, and the acidulant has good anticorrosive and mildewproof effects, and is long in quality guarantee period, free from residues, free from drug resistance and nonhazardous.