The present invention discloses the applications of a low molecular polypeptide ZY4 in preparing drugs for anti-acnes, anti-infection, anti-cancer and cosmetics. The low molecular polypeptide ZY4 comprises 17 amino acid residues, with a molecular weight of 2374.0 Da, an isoelectric point of 10.74, and an amino acid sequence of SEQ ID NO:1. The low molecular polypeptide ZY4 in the invention is artificially synthesized, with the advantages of small molecular weight and convenient artificial synthesis. The experiments have showed that the polypeptide ZY4 has obvious antibacterial effect and has significant therapeutic effect on acnes. The polypeptides can inhibit the growth of tumor cells and kill the tumor cells. The low molecular polypeptide ZY4 can be used in the preparation of medicaments or cosmetics having the effect of anti-infective, anti-tumor or anti-acne.