Abstract: Provided are a polymyxin derivative having a general formula I structure, and a preparation method and an application thereof. The method for preparing the polymyxin derivative comprises the following steps: (1) an Fmoc-AA-OP side chain free amino group of a protected basic amino acid reacting with a halogenated resin to obtain an Fmoc-AA-OP-resin; (2) the Fmoc-AA-OP-resin being coupled one by one to obtain a linear peptide-resin; (3) the linear peptide-resin selectively removing a protective group, and carrying out solid-phase cyclization to obtain a cyclic peptide-resin; (4) the cyclic peptide-resin undergoing acidic hydrolysis and ether precipitation to obtain a crude product of a cyclic polypeptide; (5) the crude product being purified and/or salt transferred and lyophilized to obtain a pure product of the cyclic polypeptide.