Combining with microscopic observation, author analyzed mineralogical features and chemical compositions using electron probe. The Jiama garnet is concentrated in skarn, with minor in hornfels, marble and porphyry. The contents of SiO₂ and Al₂O₃ in the dark zones are higher than those in the light zones, whereas the TFeO content is opposite. Garnet formed at the early stage of skarnization and provided a favorable space for precipitation of sulfides of Cu, Mo, Pb, Zn, Au and Ag mineralization at the late stage. The mineralogical features, chemical compositions, REE components, fluid inclusion and H-O isotope of garnet indicate its contact metasomatism genesis. Therefore, it is concluded that the Jiama ore deposit is a typical magma-derived hydrothermal contact metasomatism skarn type copper polymetallic deposit.