Sulfur hexafluoride（SF

6

）

as the commonly used insulating gas

has high global warming potential.Iodotrifluoromethane（CF

3

I） is a potential alternative to SF

6

which has the relatively high price and boiling point.So the gas mixtures with low proportion CF

3

I may avoid these problems and have better application prospects.We studied the breakdown voltages of CF

3

I-CO

2

gas mixtures with low proportion of CF

3

I in extreme non-uniform electric field.The tests covered different mixing ratios

different gas pressures

and different gap distances.The results show that the minute quality of CF

3

I c

an significantly increase the breakdown voltage and become stabilized while the proportion of CF

3

I is more than 6%.Though it is still lower than SF

6

the gases mixtures of CF

3

I and CO

2

have shown a good positive synergistic effect with minute quality of CF

3

I

thus the low proportion CF

3

I gas mixtures have application feasibilities and cost advantages in large gap distance system.