The thermal properties of the insulating gas in a gas insulated metal-enclosed transmission line （GIL） will affect the overall insulation performance of the GIL.At present

domestic and foreign research on the application of C

4

F

7

N/CO

2

mixed environmentally friendly gas to GIL has just started

and its thermal characteristics are still un

clear.Therefore

we established a temperature-fluid multi-physical field coupling simulation model for the environment-friendly UHV C

4

F

7

N/CO

2

mixed gas GIL and conducted simulation research.An on-site temperature rise test to effectively verify the model was also conducted.The research results indicate that the internal temperature gradient of environmental-friendly GIL is larger than that of SF

6

GIL

which should be paid attention to in the subsequent design of environmental-friendly GIL.The convection performance of SF

6

is better than that of C

4

F

7

N/CO

2

mixed gas

which will cause differences of temperature distribution in GIL.The relationship between the temperature rise of GIL center conductor and the top of the C

4

F

7

N/CO

2

GIL shell is explored

and the GIL conductor-case temperature rise response coefficient is defined.This coefficient can be applied to the subsequent center conductor temperature monitoring system based on the shell temperature.