As a typical substitute gas to SF

6

C

4

F

7

N has received wide attention in this field due to its excellent

insulation performance. Aiming at the performance degradation after multiple breakdown discharges of C

4

F

7

N-CO

2

gas mixture in this paper

the power-frequency voltage breakdown tests of C

4

F

7

N-CO

2

gas mixture under different ratio conditions are carried out under the needle plate electrode

and the decomposition products after multiple breakdown discharges of the gas mixture are detected by gas chromatography mass spectrometry. It is found by the study that the multiple breakdown voltage of C

4

F

7

N-CO

2

gas mixture will degradate. In addition

with the increase of numbers of the breakdown of C

4

F

7

N-CO

2

gas mixture

the decomposition product Hexafluoroethane C

2

F

6

increases significantly

and the content of other decomposition products is relatively low. The content of CF

2

=CFCN

CF

3

CHFCN and CF

3

CH (CF

3

) CN also increases

and correspondingly

the content of C

4

F

7

N decreases.