SF

6

has been used widely in electric power and other industries due to its perfect insulation characteris-tics and arc extinguishing performance.However

since its serious greenhouse effect

the study on its substitute gashas become a research hot spot in this field in recent years.Perfluoroisobutyronitrile（C

4

F

7

N）and its gas mixturehave attracted extensive attention by scholars both at home and abroad due to their excellent insulation performanc

eand low greenhouse effect.At present

the study on the decomposition characteristics of C

4

F

7

N and its gas mixture atdischarge conditions is rare

and the decomposition characteristics and decomposition components of its insulatinggas are very important for the insulation deterioration mechanism and state evaluation of electrical equipment.Therefore

in this paper

with comprehensive consideration of such factors as insulation strength and liquefactiontemperature

C

4

F

7

N/N

2

gas mixture is taken as the study object.The main basic decomposition path C

4

F

7

N/N

2

gasmixture is studied deeply by the use of density functional theory（DFT）

and the main decomposition reaction rateconstant is calculated with combination of the transition state theory（TST）.It is expected that the study results lay atheoretical foundation for further insulation state evaluation and study of C

4

F

7

N gas insulated electrical equipment.