The invention discloses a composite probiotic culture and a preparation method thereof. The composite probiotic culture is prepared from 3.7-5.0 kg of bean meal, 2.5-3.5 kg of corn protein meal, 9.0-10.5 kg of corn flour, 16.0-19.5 kg of bran, 9.0-11.5 kg of wheat middlings and red dogs, 4.5-6.5 kg of molasses, 3.4-5.2 kg of composite probiotic liquid and 36.0-55.0 kg of water. The preparation method comprises the steps of preparation of the composite probiotic liquid, solid fermentation and the like. The composite probiotic culture and the preparation method thereof have the advantages of being capable of increasing the feed digestion rate of dairy cattle, increasing the milk yield of the dairy cattle and reducing the breeding cost.