We introduce the development history and application scope

characteristics of gas insulated transmission line（GIL）

and GIL application status at home and abroad

and analyzed the application status of the first generation GIL using SF

6

and the second generation GIL using SF

6

gas mixtures.It is proposed to use 10%-20% SF

6

gas mixtures as the development direction of the second generation GIL.We find that the insulation using the compressed air is not applicable for high voltage and above level GIL

and put forward that the CF

3

I gas mixtures are as the research and development direction of the third generation GIL.Studying the insulation strength

the liquid temperature and the greenhouse effect

we point out the CF

3

I and N

2

mixed gas can b

e used as a replacement of SF

6

gas in GIL

the CF

3

I gas mixtures has bigger advantages in the dielectric strength

liquefaction temperature and cost

and the CF

3

I gas mixtures of 10%

3

0%CF

3

I content are applicable in researching the feasibility.