The research of friendly environmental insulation gases has great social significance. The mixture of C

4

F

7

N or C

5

F

10

O is the most potential alternative to SF

6

. GWP value

liquefaction and insulation performance of C

4

F

7

N/CO

2

and C

5

F

10

O/C

6

F

12

O/Air are studied. GWP value of C

4

F

7

N/CO

2

（total pressure 7 bar

C

4

F

7

N 0.466 bar）is 503

which is 2.13% of SF

6

;GWP value of C

5

F

10

O/C

6

F

12

O/Air(total pressure 8 bar

C

5

F

10

O 0.285 bar

C

6

F

12

O 0.100 bar)is 0.33

which is 0.001% of SF

6

. The boiling temperature of C

4

F

7

N and C

5

F

10

O are relatively high. The saturated vapor pressure of C

4

F

7

N is 0.466 bar at-25 ℃. The saturated vapor pressure of C

5

F

10

O is 0.285 bar at-5 ℃. The mixtures of C

4

F

7

N/CO

2

and C

5

F

10

O/air are positive synergistic effect gas

and have impulse voltage characteristics and are more sensitive to the negative impulse voltage. Under the lightning impulse withstand voltage of 1 425 kV

the maximum electric field strength of 420 kV busbar is 20.4 kV/mm. C

4

F

7

N/CO

2

（C

4

F

7

N partial pressure 0.466 bar

minimum function gas total pressure 7 bar）can be selected as the insulation medium to meet the low temperature environment requirement of outdoor GIS-25

℃;C

5

F

10

O/C

6

F

12

O/Air(C

5

F

10

O partial pressure 0.285 bar

C

6

F

12

O partial pressure0.100 bar

minimum function gas total pressure 8 bar)can be selected as the insulation medium to meet the low temperature environment requirement of indoor GIS-5 ℃. The results of this paper provide reference for the further development of friendly environmental GIS.