In　order　to　further　reveal　the　influences　of　barrier　dimensions　on　the　withstand　voltage　levels　of　gas　insulated　gaps,　we　experimentally　investigated　the　AC　withstand　characteristics　of　air　insulated　rod-plane　gaps　before　and　after　introducing　the　barriers　of　different　dimensions.　Moreover,　by　varying　different　barrier　positions　and　gap　distances,　we　investigated　the　barrier　effects　with　different　dimensions　on　the　AC　breakdown　voltages　and　corona　onset　voltages,　as　well　as　the　effects　of　the　residual　charges　on　barrier　surfaces　on　the　breakdown　voltages.　The　results　show　that　the　breakdown　voltage　is　significantly　increased　by　the　presence　of　a　barrier.　With　a　large　barrier　inserted,　the　breakdown　voltage　level　is　even　increased　up　to　about　2.32　times　of　that　without　a　barrier.　The　corona　onset　voltage　is　slightly　decreased　under　the　effect　of　the　barrier　with　a　maximum　decreased　voltage　about　2　kV.　The　residual　charges　on　barrier　surfaces　always　have　no　accumulative　effect　on　the　breakdown　voltages.　In　order　to　achieve　the　best　performances　concerning　to　the　global　AC　withstand　characteristics,　the　effects　of　barrier　dimensions　and　positions　on　the　breakdown　voltages　and　corona　onset　voltages　should　be　synthetically　considered.　©　2018,　High　Voltage　Engineering　Editorial　Department　of　CEPRI.　All　right　reserved.