The invention relates to a method for preparing rapeseed peptide by mixed-strains liquid fermentation. The functions of hydrolyzing protein and degrading glucosinolate of microorganisms are given fullplay, and the content of soluble nitrogen and the bioactivity of the product can be effectively increased. The method for preparing the rapeseed peptide by mixed-strains liquid fermentation includesthe following steps: (1) powder of rapeseed dregs is mixed with nutrient solution to prepare a liquid fermentation culture medium; (2) Actinomucor elegans and Aspergillus usamii are led into the liquid fermentation culture medium to be processed by liquid fermentation; (3) the fermented liquid culture medium is processed by solid-liquid separation to obtain the crude extract of rapeseed peptide; and (4) the crude extract is purified to obtain the rapeseed peptide. The invention has the advantages of simple preparation process and low cost; and during the mixed fermentation of different microorganisms, various metabolites and enzymes are generated, restriction enzyme cutting sites are different, and the functions of hydrolyzing the protein and degrading the glucosinolate of the microorganisms are given full play, thereby effectively degrading toxic substances in seeds of the rapeseed dregs, hydrolyzing the protein, and increasing the content of soluble nitrogen, the bioactivity and theyield of rapeseed peptide of the product.