With a view to study an alternative insulating gas medium for SF

6

the feasibility of C

3

F

8

as a substitute gas for SF

6

was analyzed using density functional theory (DFT) from microstructure level. Two approximate Boltzmann equations were used to analyze the insulation characteristics of C

3

F

8

/CF

3

I/CO

2

ternary mixture at 300 K. The EEDF

electron group parameter and synergy effect coefficient were calculated

and the variation of these parameters with the proportion of mixed gas were analyzed. The calculated results were compared and analyzed with that of the same ratio c-C

4

F

8

/CF

3

I/CO

2

. The results show that the performance of C

3

F

8

environmental ternary gas mixtures is better than that of c-C

4

F

8

ternary gas mixture in terms of diffusion coefficient and electron drift velocity when the reduced electric field intensity E/N is lower than 418 Td. When the ratio of C

3

F

8

is less than 7%

the insulation strength of the mixture is higher than 30%SF

6

/70%CO

2

. The gas mixture has a certain application potential in medium and low pressure equipment. Furthermore

the synergistic effect of ternary mixture is the best when the proportion of C

3

F

8

is 10%. This study theoretically verified the possibility of C

3

F

8

/CF

3

I/CO

2

replacing SF

6

.