The crystal and surface electronic properties of minerals are fundamentally linked to their flotation behavior. To investigate the effects of Ni substitution for Fe in pyrrhotite on the crystal and surface properties, as well as its oxidation by O2, density functional theory (DFT) was employed to analyze these changes at a microscopic level in both monoclinic and hexagonal pyrrhotite. The findings reveal that Ni substitution increases electron activity in monoclinic pyrrhotite, enhancing its resistance to oxidation by O2, while also strengthening the interaction between Ni-substituted monoclinic pyrrhotite and butyl xanthate. Conversely, in hexagonal pyrrhotite, Ni substitution enhances electron stability but makes it more susceptible to oxidation by O2 and weakens its interaction with butyl xanthate. Understanding the electronic properties and interaction mechanisms of Ni-substituted pyrrhotite with O2 is crucial for elucidating the surface oxidation mechanisms of pyrrhotite. This research offers insights and guidance for optimizing pyrrhotite flotation processes.