The invention provides a preparation method of a traditional Chinese medicine fermented feed additive capable of improving production performance of broilers. The preparation method comprises the steps as follows: (1) preparation of Danggui Buxue Tang (DBT) medicine powder; (2) preparation of a fermentation medium; (3) activation of bacillus subtilis and preparation of a seed solution; and (4) fermentation: the fermentation medium is inoculated with the seed solution for shaking table fermentation culture at 37 DEG C. The invention further provides the traditional Chinese medicine fermented feed additive prepared by the method. The method for fermenting the DBT by a bacillus subtilis liquid is adopted, by 42 d of feeding tests and related index determination, addition of 1.0% of DBT fermented product to ration can significantly promote growth performance, immune functions and oxidation resistance of white feather broilers and has significant effects on mucous membrane structures of small intestines, the feeding effects are remarkably superior to a non-fermented group and a blank control group, and the traditional Chinese medicine fermented feed additive can be widely applied to thelivestock and poultry breeding industry as a novel feed additive.