Because of its excellent insulation and arc quenching performances,SF_6 is widely used in the power system such as in switchgear equipment. Because of its high global warming potential,reducing its usage or replacing SF_6 has become a focus from many researchers and a heat topic in the field of switchgear. The application of dry air as the insulation gas in SF_6 -free gas insulated switchgear and some related issues are discussed in this paper,including the insulation property of dry air,comparison of dry air with other insulation gases,the required humidity in the utilization of dry air,the detection of gas leakage,and the basic principles used in disconnector to interrupt bus bar transferring current. The paper provides technical basis for dry air insulated switchgears.