Effect of oxygen and Na₂S on the flotation of cuprite was invested by flotation test, FESEM, EMPA and XPS. The micro-flotation experiments indicated that the flotation recovery of cuprite can be greatly increased by adding an appropriate amount of Na₂S. FESEM showed that numerous fragments were covered on the cuprite surfaces after sulfidization, and the shapes of these fragments were more regular and complete with the Na₂S concentration of 5.0×10^-4 mol/L. EPMA and EDS analysis confirmed that these fragments were newly-formed copper sulfide species, which was the key to promoting the flotation of cuprite. XPS analysis revealed that the sulfidization process of cuprite was that Na₂S first underwent an oxidation-reduction reaction with the CuO on its surface, which was due to the extremely easy oxidation of the surface of cuprite. The Cu²⁺ was reduced to Cu⁺, and S^2- was mainly oxidized to (S₂)^2- and (S_n)^2-.