The invention discloses a feed additive for increasing the egg yield of hens and a preparation method thereof. The feed additive is prepared by fermenting the following traditional Chinese medicine raw materials of radix codonopsis, poria cocos, bighead atractylodes rhizome, malt, medicated leaven, semen cuscutae, epimedium and common cnidium fruit with lactobacilli, bifidobacteria, microzyme and bacillus subtilis. For the feed additive for increasing the egg yield of the hens, disclosed by the invention, traditional Chinese medicine components are compounded with microorganisms to form a composite traditional Chinese medicine micro-ecological preparation to be used as the feed additive, so that the number of beneficial bacteria can be increased, the ecological balance of intestinal tracts of organisms can be maintained, the growth of harmful bacteria is restrained, and the health of the intestinal tracts of the organisms can be improved; macromolecular substances, such as starches and proteins, in the feed, can be effectively decomposed, small molecular nutrient substances which are easy to digest and absorb for laying hens are released, and the utilization rate of the feed is increased; the egg laying rate, the production performance and the reproductive performance are obviously improved, the quality of eggs is improved, and the peak period of egg laying is prolonged; and the toxic substance is decomposed in the fermentation process, and the feed additive dost not have medicine residue and is free of toxic and side effects, so that the feed additive is safe and reliable.