The invention provides a water-soluble amino acid segmented copolymer, and a preparation method and application thereof. The amino acid segmented copolymer has the structure shown as a formula I or formula II shown as the accompanying drawing; R1 is a hydrogen, an alkyl group or a substituted alkyl group; R2 is -NH- or R5(CH2)rNH-; R3 is one or a plurality of groups of a hydrogen, a hydrophobic group and an active drug group; R4 is benzyl, cholesterol formylm, acetyl, a cholic acid group, a deoxidized cholic acid group or C4-C20 alkyl groups. The amino acid segmented copolymer is a polypeptide copolymer with excellent water solubility, and can be used in the field of delivery of biological materials such as drug. After freeze-drying, the material has a good re-dissolving effect; the defect of poor water solubility of macromolecule materials or macromolecule nanometer drug in the prior art can be overcome. The material contains the hydrophobic group through modification or is chemically bonded with drug with biological activity; the modified macromolecule material or the bonded drug can still maintain excellent water solubility and re-dissolving capability; the potential application prospect is realized in the field of biological materials.