The invention provides a biological fermentation feed taking weakly washed chicks as a main raw material, which is obtained by taking weakly washed chicks and molasses beancurd skin as fermentation base materials and carrying out solid fermentation on the fermentation base materials by using compound probiotics. The compound probiotics are two or more of saccharomycetes, lactobacillus plantarum and lactobacillus reuteri. The weight ratio of the weakly washed chicks to the molasses bean curd skin is 1: (1.5-3.5). According to the application of the biological fermentation feed taking the weakly washed chicks as the raw material, the addition amount of the biological fermentation feed in a breeding field is 4-20%. According to the invention, the high-quality animal protein source of the weakly washed chicks in the hatchery, the oligosaccharide prebiotics of the by-product molasses beancurd skin of the oil plant and the good adsorbability of the chicks and the oligosaccharide prebiotics are fully utilized and are subjected to mixed fermentation to prepare the high-quality fermented feed, so that the resources are efficiently utilized in a high-quality manner, the high-quality raw materials are prevented from being treated as organic fertilizers, the price is low, and the market prospect is wide.