Due to its high greenhouse effect, the use of SF₆ as the main insulating gas is restricted in the electric power field. Along with the aim of environmental protection, the search for new alternative gases with a lower greenhouse effect and higher insulation strength has received a lot of attention. The properties of alternative gases have a vital impact on the performance of medium-voltage power distribution equipment. Firstly, based on the existing liquefaction temperatures of SF₆/N₂, SF₆/CO₂, and SF₆/CF₄, the calculated liquefaction temperatures were expanded to 0.7 MPa. Combining the Antoine vapor-pressure equation and the basic law of vapor–liquid balance, the vapor pressures of SF₆/N₂, CF₃I/N₂, c-C₄F₈/N₂, C4-PFN/N₂, C4-PFN/CO₂, and C5-PFK/CO₂ were obtained. Secondly, the critical breakdown field strength was analyzed for C4-PFN/CO₂, C5-PFK/CO₂, SF₆, CF₃I/N₂, C5-PFK/Air, and c-C₄F₈/N₂. Finally, the GWPs of SF₆/N₂, C4-PFN/N₂, C4-PFN/CO₂, C5-PFK/CO₂, and C5-PFK/N₂ were discussed. The results show that the liquefaction temperature gradually decreases as the pressure rises; SF₆/N₂ has the highest vapor pressure at −5 °C; the critical breakdown field strengths of several mixtures are higher than that of SF₆.