The research on the thermodynamic properties of environmentally friendly insulating medium C

4

F

7

N and its mixed gas has reference value for understanding its application range and application prospects. Consequently

we calculated the saturated vapor pressures of C

4

F

7

N/CO

2

and C

4

F

7

N/N

2

under different mixing ratios by the Riedel vapor pressure equation and Raoult’s law. The compressive factors and densities of C

4

F

7

N/CO

2

and C

4

F

7

N/N

2

were calculated based on the P-R equation of state. According to the molecular structure characteristics

the constant pressure specific heat capacity and viscosity of the two mixed gases were calculated by the Joback group contribution method and Thodos method. The calculation results show that if the liquefaction temperature of the insulating medium is not higher than 253 K when the GIS and GIL are operated at 0.5 MPa

the molar fraction of C

4

F

7

N in the mixed gas should not exceed 8% and10%

respectively

the global warming potential of each of the mixed gases is about 2.45% and 3.83% of SF

6

and the greenhouse effect is negligible. Under the above conditions

the two mixed gases tend to be in an ideal gas state

and the compression factor is close to 1. The content of C

4

F

7

N in the two mixed gases is small

but the contribution of the mixed gas to the specific heat capacity is larger

and the contribution to the viscosity is smaller. The calculation results in this paper can provide basic data for the quenching characteristics of C

4

F

7

N/CO

2

and C

4

F

7

N/N

2

environmentally friendly mixed gases and their application in GIS and GIL.