The present invention discloses a micro-ecological preparation for improving milk yields of dairy cows, and belongs to the preparation for improving the milk yields of the dairy cows. The micro-ecological preparation uses a method combining statistical methods with culture-independent technology to screen dominant bacteria in rumens of high-yielding dairy cows; pure strains are obtained from the dominant bacteria by using pure culture technology; and the micro-ecological preparation is prepared through fermenting, culturing, combining and mixing the pure strains. The micro-ecological preparation is prepared by following specific steps: (1) sequencing, (2) screening, (3) separating and purifying strains, (4) culturing, (5) fermenting (6) mixing and (7) packaging. The micro-ecological preparation contains Bacteroidaceae and Ruminococcus helpful for decomposing polysaccharide and cellulose, can improve Bacteroidaceae and Ruminococcus contents in rumen bacteria of the high-yielding dairy cows in order to ensure the advantage position and improve the utilization of the cellulose and the polysaccharide, thus improving absorption and utilization of feed nutrient components for the dairy cows, increase the milk yields and bring economic benefits. The Bacteroidaceae can help the host absorb the polysaccharide, improve nutrition utilization rates and host's immunity, and maintain gastrointestinal micro-ecological balance. The micro-ecological preparation has a strong pertinence and specificity.