SF6, due to its excellent electrical properties, has been widely used in the electrical industry and remains the best gaseous insulation material to date. However, with its extremely high global warming potential (GWP), it is one of the major contributors to global climate change. Researchers have extensively studied SF6 alternative gases over the past few decades. Unfortunately, many alternative gases have their own drawbacks and limitations, making them difficult to apply in practice. This paper first analyzes the saturated vapor pressure characteristics of C4F7N and selects the partial pressures of C4F7N in the mixed gas as 20 kPa and 40 kPa, obtaining liquefaction temperatures of −40 ℃ and −27 ℃, respectively, which can meet the actual operational requirements of GIS equipment. Subsequently, through lightning impulse experiments, the effects of different partial pressures, total pressures, and other factors on the insulation characteristics of the mixed gas are systematically investigated. The results indicate that the C4F7N mixed gas possesses sufficient insulation strength and liquefaction temperature, enabling its potential as a substitute for SF6.