Abstract: In order to evaluate the insulation properties of CF₃SO₂F/N₂ mixtures, their ionization characteristics in the electric field were studied. The effective ionization coefficient and critical reduction field strength of CF₃SO₂F/N₂ mixture were obtained by steady-state Townsend experiment (SST), and the effects of mixing ratio, reduction field strength, and electrode distance on their ionization characteristics were studied. The insulation strength of CF₃SO₂F/N₂ gas mixtures relative to SF₆ was compared. The results show that the ionization characteristics of CF₃SO₂F/N₂ gas mixtures are similar to those of N₂ when the molar fraction of CF₃SO₂F is 10%. As the proportion of CF₃SO₂F increases to more than 20%, the ionization characteristics of CF₃SO₂F/N₂ gas mixtures are gradually dominated by CF₃SO₂F. The theoretical dielectric strength of CF₃SO₂F/N₂ gas mixtures relative to SF₆ increases with the increase of CF₃SO₂F molar fraction, and the critical reduced field strength of 40% CF₃SO₂F/60% N₂ gas mixtures is about 1.01 times that of SF₆, however, its sensitivity to electric field changes is not as good as that of SF₆. The results can provide a theoretical basis for the evaluation of the dielectric strength of CF₃SO₂F/N₂ gas mixtures.