The invention relates to the technical field of polypeptides, and discloses a synthetic polypeptide and a synthesis method and application thereof. The amino acid sequence of the synthetic polypeptideis as shown in SEQ ID NO:1, or one or two or more amino acids are substituted, deleted or added on the sequence shown in the SEQ ID NO:1, and the polypeptide has UV injury resistance activity. The invention provides a novel active heptapeptide. The survival rate of incubated skin cells is increased by 20% under the high-dose UVA irradiation injuries, the cell cycle G2 phase is prolonged, and vigorous growth and value-added states are presented. The synthetic polypeptide can be applicable to various beauty and skin care products, health care products and medical products, harm of ultraviolet rays to human body tissue is reduced, and the effects of protecting the skin and delaying senescence are achieved.