The application of a peptide having sequence of formula I or its derivant in preparing the medicine for preventing or treating liver damage, especially liver damage and hepatitis C is disclosed, Xaa1-Gln-Xaa2-Xaa3-Thr-Ser-Gly-Xaa4 (formula I) wherein, Xaa1 is deletion, Ala, Gly, Val, Leu or Ile, Xaa2 is Thr or Ser, Xaa3 is Tyr, Phe or Trp, and Xaa4 is deletion, Ala, Gly, Val, Leu, Ile or Pro. The composite medicine containing the said peptide, its preparation method, and the polynucleotide for coding the said peptide are also disclosed.