Abstract: With the continuous development of mineral resources to high altitude areas, the study of sulfide ore flotation in unconventional systems has been emphasized. There is a consensus that moderate oxidation of sulfide ore is beneficial to flotation, but the specific suitable dissolved oxygen value is inconclusive, and there are few studies on sulfide ore flotation under low dissolved oxygen environment at high altitude. In this paper, we designed and assembled an atmosphere simulation flotation equipment to simulate the flotation of pyrite at high altitude by controlling the partial pressure of N₂/O₂ and dissolved oxygen under atmospheric conditions. X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), Fourier transform infrared spectrometer (FT-IR), UV-vis spectrophotometer, zeta potential, and contact angle measurements were used to reveal the effects of surface oxidation and agent adsorption on pyrite at high altitude (4600 m dissolved oxygen (DO) = 4.0 mg/L). The results of pure mineral flotation indicated that the high altitude and low dissolved oxygen environment is favorable for pyrite flotation. Contact angle measurements and XPS analysis showed that the high altitude atmosphere slows down the oxidation of pyrite surface, facilitates \rm S_n^2- /S⁰ production and enhances surface hydrophobicity. Electrochemical calculations and zeta potential analysis showed that the influence of atmosphere on the form of pyrite adsorption is small, and the different atmospheric conditions are consistent with dixanthogen electrochemical adsorption, with lower Zeta potential under high altitude atmosphere and significant potential shift after sodium isobutyl xanthate (SIBX) adsorption. The results of FT-IR, UV-vis, and AFM analysis showed that SIBX adsorbed more on the surface of pyrite under high altitude atmosphere and adsorbed on the surface in a mesh structure composed of column/block. The results of the experimental study revealed the reasons for the easy flotation of sulfide ores at high altitude with less collector dosage, and confirmed that the combined DO–pH regulation is beneficial to achieve more efficient flotation of pyrite.