The invention relates to biological feed, in particular to a biological fermented feed and a preparation method thereof. The method consists of: subjecting Aspergillus niger, Bacillus licheniformis, Bacillus coagulans, Bacillus subtilis, Lactobacillus plantarum, and Candida utilis respectively to two-stage liquid fermentation culture, and then conducting three-stage solid fermentation culture to obtain fermented culture, i.e. biological feed. The fermented culture provided by the invention utilizes neural network, pattern recognition, genetic algorithm and other optimization methods to optimize the fermentation conditions, a biosynthesis network is constructed according to the principle of metabolic engineering, and pathway analysis and metabolic flux control are carried out on the synthetic network on the basis, and enzymolysis, anaerobism, aerobiosis, bacterium cultivation and other processes are employed, thus increasing the protein content, reducing the content of crude fiber, improving the palatability and fragrance, increasing probiotics, and removing toxins from feed raw materials.