Abstract: The depression mechanism of sulfite ions on sphalerite and Pb²⁺ activated sphalerite in the flotation separation of galena from sphalerite still lacked in-depth insight. Therefore, the depression mechanism of sulfite ions on sphalerite and Pb²⁺ activated sphalerite in the flotation separation of galena from sphalerite was further systematically investigated with experiments and density functional theory (DFT) calculations. The X-ray photoelectric spectroscopy (XPS) results, DFT calculation results, and frontier molecular orbital analysis indicated that sulfite ions were difficult to be adsorbed on sphalerite surface, suggesting that sulfite ions achieved depression effects on sphalerite through other non-adsorption mechanisms. First, the oxygen content in the surface of sphalerite treated with sulfite ions increased, which enhanced the hydrophilicity of the sphalerite and further increased the difference in hydrophilicity between sphalerite and galena. Then, sulfite ions were chelated with lead ions to form PbSO₃ in solution. The hydrophilic PbSO₃ was more easily adsorbed on sphalerite than galena. The interaction between sulfite ions and lead ions could effectively inhibit the activation of sphalerite. In addition, the UV spectrum showed that after adding sulfite ions, the peak of perxanthate in the sphalerite treated xanthate solution was significantly stronger than that in the galena with xanthate solution, indicating that xanthate interacted more readily with sulfite ions and oxygen molecules within the sphalerite system, leading to the formation of perxanthate. However, sulfite ions hardly depressed the flotation of galena and could promote the flotation of galena to some extent. This study deepened the understanding of the depression mechanism of sulfite ions on sphalerite and Pb²⁺ activated sphalerite.