The invention discloses a preparation method of a lactating sow feed. The preparation method comprises the following specific steps: soaking soybeans in water, grinding the soaked soybeans into thick liquid by a grinding miller, raising the temperature, cooking and cooling to prepare soybean milk dregs; mixing the soybean milk dregs, alfalfa meal, corn flour, brown sugar, a composite bacterial liquid and a compound enzyme according to a ratio; carrying out solid fermentation and enzymolysis, and then drying the substance to obtain a soybean-grass fermentation material; uniformly mixing the soybean-grass fermentation material, corn, broken rice, bean pulp, fish meal, emulsified oil powder, helianthus tuberosus powder, seaweed, composite Chinese herbal medicines and 4% of premix sold in the market, so as to obtain the lactating sow feed capable of calling food, promoting lactation and resisting constipation. The lactating sow feed disclosed by the invention is rich in emulsified fat, yeast protein, active oligopeptide, short-chain dextrin, glucose, soybean and helianthus tuberosus oligosaccharides, lactic acid, probiotics and unstated prolactin, good in palatability, balanced in amino acid, high in nutrition, low in probability of digestion, low in anti-nutritional factor content, and capable of obviously promoting sow ingestion, simulating lactation and preventing constipation.