C

6

F

12

O has attracted extensiv

e attention from scholars in the field of SF

6

substitution gas both at homeand abroad due to its excellent insulation performance and environmental protection characteristics.For exploringthe optimal application scheme of C

6

F

12

O gas mixture

the influence of O

2

on the insulation performance and decom-position characteristics of C

6

F

12

O/CO

2

gas mixture is studied.The gas power frequency breakdown test platform isset up to study the power frequency breakdown test of C

6

F

12

O/CO

2

gas mixture with different O

2

mixing ratio and dif-ferent gas pressure.The decomposition products of the gas mixture after 150 times of power frequency breakdownare analyzed qualitatively and quantitatively by gas chromatography-mass spectrometry（GC-MS）and

at the sametime

the change of the amount of solid released on the electrode surface after breakdown is observed.In addition

the mixture ratio and pressure range of O

2

of C

6

F

12

O/CO

2

gas mixture for projects are discussed.It is shown by thestudy result that adding 3%～7%O

2

to the C

6

F

12

O/CO

2

gas mixture can better improve the gas insulation performance.Moreover

in case of breakdown discharge

adding O

2

can be able to inhibit the solid carbon release and reduce thevolume fraction of C

3

F

6

a kind of highly toxic substance.However

it will promote the decomposition of C

6

F

12

O andincrease the content of CF

4

C

2

F

6

COF

2

and CO.It is concluded after comprehensive consideration of the insulationperformance and decomposition characteristics that the C

6

F

12

O-CO

2

-O

2

gas mixture at gas pressure at 0.1～0.18 MPa and 3%～5% O

2

mixing ratio has certain engineering practical value.