Abstract: The contact interface of electrical connector often occurs serious failures due to wear, so it is necessary to study the fretting wear behavior in electrical contact mode. Based on the difference of ambient oxygen concentration (10%, 20%, 30%) in electrical contact mode, this paper focused on the effect of oxygen concentration on fretting wear behavior and wear mechanism of copper/brass. It indicated that the stable values of friction coefficient corresponding to oxygen content of 10%O₂, 20%O₂ and 30%O₂ in the environment were 0.77, 0.71 and 0.80, respectively. The result of friction dissipation energy was consistent with that of wear volume, i.e. the highest in 10%O₂ environment, the second in 30%O₂ environment, the lowest in 20%O₂ environment. It can be inferred that the damage under the condition of lowest oxygen content was more serious than that under the condition of high oxygen content. It can be seen from the electrical contact life that the electrical contact performance was the best with 20%O₂, the second with 10%O₂ and the worst with 30%O₂.The fretting wear zone was oxidized in varying degrees under different oxygen concentrations, theoretically, the more sufficient the oxygen content, the more serious the oxidation. Among them, the fretting wear resistance was the worst in 10%O₂ environment and the electrical contact performance was the worst in 30%O₂ environment; while the electrical contact performance and wear resistance were the best 20%O₂ environment. The results showed that there was a nonlinear dependence between the electrical contact performance and the oxygen concentration in the atmosphere. The oxidation wear was the most serious at 30% oxygen concentration, the microstructure was coarse and agglomerated oxide particles which resulted in the higher contact resistance than the other two oxygen concentrations. However, more debris induced by fretting wear was easy to be oxidized at lower concentration with 10%, so the contact resistance was higher than oxygen concentration with 20% and less than oxygen concentration with 30%, the fresh wear debris was loosely covered in the wear scar indicating that the oxygen content and wear debris dominated jointly the electrical contact performance and wear behavior of copper. Combined with the results of white-light interferometry, scanning electron microscope and electron probe microanalysis, it was found that the wear mechanisms under different oxygen concentrations were mainly oxidation, material transfer and delamination.