In　order　to　achieve　higher　temperature　measurement　accuracy　and　improve　the　requirement　of　radiation　characteristics　of　the　antenna,　high　directional　small　diameter　antenna　is　designed　for　human　body　temperature　measurement　by　microwave　radiometer.　The　antenna　frequency　band　is　6~12GHz,　the　gain　is　higher　than　12dB,　the　diameter　is　more　than　20dB,　the　maximum　cross　polarization　level　is　less　than　-25dB,　The　E-plane　and　H-plane　are　symmetrically　distributed,　and　the　input　standing　wave　ratio　is　less　than　1.5dB.　In　this　paper,　the　Angle　horn　size　and　directionality　calculation　formula　were　calculated　to　obtain　the　angle　horn　size,　the　ridge　waveguide　and　ridge　curve　calculation　formula　were　used　to　calculate,　to　obtain　the　dual-ridged　horn　size,　and　the　modeling　simulation　in　Comsol　simulation　software,　to　determine　the　optimal　size.　The　simulation　results　of　the　broadband　horn　antenna　show　that　the　gain,　backward　and　forward　rejection　ratio,　standing　wave　ratio　and　other　parameters　are　good,　which　is　in　line　with　the　design　objectives,　and　provides　a　solid　foundation　for　further　study　of　microwave　radiometer　temperature　measurement.　©　2023　IEEE.