Abstract：The Dajing Cu-Sn polymetallic deposit is characterized by its large size, many associated elements, narrow and dense ore veins and high grades. However, no Yanshanian intrusions were found within the limits of the ore field, so the genesis of the deposit is in controversy. From a viewpoint of mantle branch tectonics, the deposit is situated at the core of the Da Hinggan Mountains mantle branch, and the multiple evolution of the mantle hot plume linked up the deep hydrothermal ore fluids. The ore fluids extracted some ore materials on the way, which concentrated in favorable structural fractures and formed the deposit. The orientation of ore-controlling fractures is closely related with the regional structural stress field during mineralization. The zoning of the ore-forming elements Sn, Cu, Au, Ag, Pb and Zn within the deposit should be related to mineralization and crystallization temperatures of ore materials. The mineralizations of the elements such as Sn, Cu and Au, which crystallized under higher P-T conditions, are in the center of the ore field; whereas the mineralizations of the elements such as Ag, Pb and Zn, which crystallized under lower P-T conditions, were mostly localized in the surroundings of the deposit.