The invention discloses brucella L7/L12 protein antigen epitope polypeptides and an application thereof. The polypeptides comprise a polypeptide having an amino acid sequence containing SEQ ID NO.1 or a sequence shown in the SEQ ID NO:1 and formed by substitution and/or deletion of one or/and a plurality of amino acid residues, and also can be a derivative polypeptide having the amino acid sequence being a sequence shown in the SEQ ID NO:1 and having addition of a brucella immunogenicity function. A recombinant vector or expression cassette or transgenic cell or recombinant bacteria can be composed of the SEQIDNO.1 polypeptides. The application of the polypeptides in preparation of reagents or drugs for diagnosis or prevention or treatment of diseases caused by brucella is provided. The screening polypeptides are chemically synthesized; after DC stimulation, high-concentration IL-4 can be released and can be used as a target antigen for detection of serum infected by brucella, or an antigen for preparation of an L7/L12 protein monoclonal antibody.