The invention relates to a high-efficiency and environment-friendly feed additive for livestock and poultry and a preparation method thereof. The feed additive comprises the following components in percentage by weight: 80-90 percent of microbial ecological agent, 5-10 percent of oligosaccharides and 5-10 percent of phytase. The feed additive can promote the growth of livestock and poultry, improve the feed intake and the feed efficiency, adjust the immunologic function of the livestock and poultry, enhance the ability to resist disease, replace antibiotics to reduce the diarrhea rate and reduce nitrogen and phosphor discharge as well as ammonia emanation in feces, the pollution of extreta to the environment and the costs on feed and cultivation.