The invention relates to isolation, identification and application of a Fabricius bursa active hexapeptide for promoting an immunoreaction of avian influenza and/or a Newcastle disease bivalent vaccine. The Fabricius bursa active hexapeptide has an amino acid composition of Lys Gly Asn Arg Val Tyr, has a simple structure and is extremely weak in immunogenicity. The active peptide has the functionof promoting the immune response of the vaccine and can promote the antibody reaction against the AIV antigen and the antibody reaction against the NDV antigen in the mouse in the mouse immunization experiment. The active peptide can promote the cellular immune response, improve lymphocyte viability and an antigen presentation reaction and improve the vaccine immunopotency, can be used as a vaccine adjuvant or immunopotentiator in animal vaccine application research, can improve the immune response of animal organisms to specific antigens, can improve the immune efficacy of vaccines and can improve the ability of animal organisms resisting epidemic disease infection.