Biological polypeptide for replacing plasma protein in feed

The invention relates to a biological polypeptide capable of replacing plasma protein in a feed. The biological polypeptide comprises the following components: a soybean polypeptide, a yeast hydrolysis complex and a composite microecological preparation, wherein the soybean polypeptide is prepared by the steps of deeply fermenting soybean meal by bacillus subtilis, and then adding neutral protease and performing enzymolysis; the yeast hydrolysis complex is prepared by the steps of adding water and sugar into dry yeast used as a raw material, activating, then adding an additive into an activated substance, and finally preserving heat and enzymolyzing the activated substance; and the composite microecological preparation is lactic acid bacteria and/or saccharomycetes and/or Bacillus licheniformis. The product can completely replace the plasma protein in suckling pig feeds, provide a high-quality protein raw material for the feeds, and can improve the immunity of piglets, reduce diarrhea, promote growth, reduce feed conversion ratio, and increase breeding benefit at the same time.