C6F12O has the potential to be used in gas-insulated equipment because of its excellent insulation performance and low global warming potential value. In order to study the effect of O-2 on the decomposition characteristics of the C6F12O/CO2 gas mixture, power frequency breakdown experiments were conducted on a C6F12O/O-2/CO2 gas mixture with different O-2 mixing ratios. The decomposition products of the C6F12O gas mixture after multiple breakdowns were analyzed qualitatively and quantitatively by gas chromatography-mass spectrometry. The effects of the O-2 mixing ratio, breakdown times, and effective gas production rate on the decomposition characteristics of the gas mixture were investigated. The results show that the main decomposition products are CF4, C2F6, C3F6, C3F8, C4F10, C5F12, C3F7H, and CF2O, and the addition of O-2 will promote the formation of the above several decomposition products. Except for C3F6, the concentrations of other decomposition products tend to increase and then decrease with the increase in the O-2 mixing ratio. The concentrations of CF4, C2F6, C3F6, and C3F8 increase with the times of breakdowns. The effective gas production rates of CF4, C2F6, and C3F8 show a trend of increasing and then decreasing in the process of adding O-2 to the C6F12O/O-2/CO2 gas mixture. This study provides a reference for the industrial application of the C6F12O/O-2/CO2 gas mixture.& nbsp;(c) 2021 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).