Abstract: A nutritional polypeptide having branched-structure with efficient broad-spectrum antibacterial and antifungal functions provided. The nutritional polypeptide having branched-structure is a polypeptide containing L-lysine or D-lysine moieties having a molecular weight of 3000-7000 Da. The branched-structured polypeptide has a highly efficient broad-spectrum antibacterial effect against bacteria, fungi and mycoplasma at low concentrations without developing resistance. Compared with conventional antimicrobials, the disclosed polypeptides have excellent biocompatibility, are non-cytotoxic, have no adverse effects on animals by intravenous injection, and can satisfy the requirements of intravenous antimicrobials in vivo. The degradation product is lysine, a nutrient essential to the organism, which has no toxic side effects. The branched-structured polypeptide is chemically synthesized throughout without the need of biofermentation processes, and is physically, chemically and biologically stable.