The invention discloses an antigen for detecting a sheep echinococcosis antibody and a preparation method of an agar diffusion plate, and belongs to the technical field of biological detection. The preparation method of the antigen comprises the following steps: performing enzyme digestion connection on a sheep echinococcosis EG95 protein nucleic acid sequence, and constructing the sheep echinococcosis EG95 protein nucleic acid sequence on a plasmid vector; then performing converting into escherichia coli, constructing an expression strain, performing IPTG induced expression, and performing crushing to obtain an inclusion body; and performing washing, cracking, centrifuging, purifying, dialyzing, concentrating, freeze-drying, and diluting with PBS. The preparation method of the agar diffusion plate comprises the following steps: adding water and PBS into agarose, performing heating, adding polyethylene glycol 6000, MES and sodium chloride, performing cooling, performing punching, and sealing the bottom. The antigen and the agar diffusion plate provided by the invention have the advantages of high sensitivity, strong specificity and strong universality, have good biosafety, are easyfor large-scale production, are especially suitable for clinical detection of sheep serum by grassroots veterinarians, and have wide popularization and application value.