Abstract: The invention discloses a polypeptide compound and a preparation method and application thereof. The polypeptide compound has a structural formula as follows: (XAXBXCXDXE-X)2KY, or {(XAXBXCXDXE-X)2K}2KY, or {({XAXBXCXDXE-X}2K)2K}2KY, where, XA is a polar amino acid molecule, XB and XE are alkaline amino acid molecules (the same or different), XC and XD are non-polar amino acid molecules (the same or different), K is lysine (Lys, K), and X and Y are null, or any one or more amino acid or chemical groups. The polypeptide compound provided in the invention has an effect of enhancing the immune function of a body and has an application potential of being developed into a clinical medicine capable of enhancing the immune function of a body.