To reduce the greenhouse effect of SF

6

we investigated the technology of replacing SF

6

gas insulation by environmental-friendly gas-insulated transmission line（GIL） to improve the environmental-friendly benefits of equipment. Meanwhile

we summarized the development process of environmental-friendly GIL technology

explored the compressed air GIL technology was.

and theoretically suggested the gas pressure and pipeline sizes for GIL design. The current research on SF

6

/N2 gas mixture is complete. According to the design of SF

6

GIL

the dielectric strength

insulation design and current-loading ability were obtained to guide GIL design. The products of 220～550 kV GIL with SF

6

/N2 gas m

ixture are in normal operation. And UHV GIL prototype has been developed. New environment-friendly gas C

4

F

7

N possesses favorable insulation and environment-friendly performances. 420 kV GIL with C

4

F

7

N/CO

2

gas mixture has been in test operation. There are some technical challenges in developing UHV GIL with C

4

F

7

N gas mixture. It is urged to resolve the technical problems

in order to promote the development of environment-friendly equipment.