A preparation method of a microecological culture feed additive belongs to the technical field of livestock and poultry feed additive. A solid fermentation medium comprises 40% of wheat bran, 10% of corn, 9% of soybean meal, 0.5% of urea, 0.1% of potassium dihydrogen phosphate, 0.1% of sodium dihydrogen phosphate, 0.1% of manganese sulfate, 0.2% of calcium chloride and 40% of water. fermentation strains include plant lactobacillus, bacillus subtilis and saccharomyces cerevisiae in a ratio of 1:2:2. The method comprises the following steps: crushing, sieving, mixing, disinfecting, preparing fermentation bacteria liquid, inoculating fermentation strains and obtaining a finished product. The microecological culture feed additive provided by the invention combines functions of nutrition and health care, has no toxic or side-effect or pollution, and can improve antioxidation capability and immunization function of a weaning pigling, increase daily weight gain of the pigling and forage conversion rate, reduce diarrhoea rate, reduce or prevent pigling weaning stress syndrome and substitute antibiotic additive in forage.