Various incorporation of Au in pyrite and its effects on the geometrical structure, electronic structure and flotability of pyrite were theoretically investigated and fully discussed by performing density functional theory (DFT). The calculated incorporation energy shows that gold would most likely exist in pyrite via incorporating into interstitial lattice sites in the absence of As impurity. As a result of incorporated Au, the covalence levels of the S—Fe and S—S bonds are changed, and the tonicity of Au—S bonds and antibonding of Au—Fe bonds are found to form in the pyrite, which would change the natural flotability of pyrite. The Au impurity energy levels are introduced into the energy band and result in the transformation of pyrite semiconductivity type. The calculated band-gap value suggests that the incorporated Au significantly decreases pyrite semiconductivity level, which enhances the formation and the adsorption stability of dixanthogen during pyrite flotation. The DOS results reveal that the stability and depression difficulty level of pyrites increases in the following order: Fe32S63As < Fe32S64 < Fe32S63AsAu < Fe32S64Au.