Abstract: The breakdown characteristics and decomposition characteristics of a new type of environmentally friendly insulating gas C₆F₁₂O and N₂ mixed gas under AC voltage were investigated. Firstly, the mixed ratio of C₆F₁₂O and N₂ used in equipment ratio was discussed. The breakdown performance of C₆F₁₂O and N₂ was explored under AC voltage in the quasi uniform field. Some comparisons with that of SF6 gas mixture were gotten. The decomposition gases after 100 times breakdown experiment of 3%C₆F₁₂O and N₂ were qualitative detected by GC-MS. The generation process of decomposition products was calculated by using density functional theory based on the detection results. The influence of temperature on reaction energy was analyzed and molecular orbital gap of decomposition products was gotten. The experimental results show that the breakdown voltage of 3%C₆F₁₂O and N₂ mixed gas is about 1.7 times of that of pure N₂, and is equal to that of 10%SF6 and N₂ mixed gas. The decomposition products are mainly CF₄, C₂F₆, C₃F₆, C₃F₈, C4 F10 and C5 F12. The calculation shows that the formation of decomposition reaction of energy production with the increase of temperature varied, and the decomposition of molecular orbital gap product value from large to small is in the order of CF₄, C₂F₆, C₃F₈, C₄F₁₀, C₅F₁₂ and C₃F₆. The orbital gap value of CF4 is the largest, which is 12.590 eV.