A cyclic peptide is provided, which consists of 3-15 amino acids connected together with each other, wherein the amino acids contained by the cyclic peptide can be the common amino acids or the rare ones, the natural amino acids or the artificial ones, the conformation of any amino acid can be L-type or D-type, and the connection sequence is free among the amino acids. The preferred formula (I) consists of 8 common amino acids connected with each other through peptide linkages to form a cyclic peptide, and the present invention also relates to the method to prepare the cyclic peptide and the application thereof to preparation of immune-suppressive drugs.