In this paper, we studied the dielectric breakdown voltage characteristics by the AC withstand voltage test on using green insulation dry air instead of SF6 insulation gas used in the GIB (gas insulated bus) of 362 kV GIS (gas insulated switchgear). The AC withstand voltage test applied to the standard KEPCO`s 362 kV GIB with dry air insulation, and the equivalence of dielectric breakdown voltage for dry air and SF6 gas were examined, and the empirical formulas of dielectric breakdown voltage for dry air were calculated, and the criterion of AC withstand voltage test for dry air insulation was derived. Using the criterion, dry air can be used instead of SF6 gas for 362 kV GIB in the factory acceptance test was confirmed.