In　this　article,　the　effect　of　residual　charges　on　the　lightning　impulse　voltage　testing　in　the　air　insulation　gap　and　the　hybrid　gas-solid　insulation　gap　within　the　range　of　30-50　cm　gap　distances　was　studied　using　the　modified　up-and-down　test　(UDT)　method.　The　impulse　voltage　testing　was　performed　by　changing　the　gap　distance,　the　resting　time,　and　the　initial　voltage.　Experimental　results　show　that　the　residual　charges　cause　continuous　breakdown　and　withstand　during　the　testing　when　the　gap　distance　is　30　cm,　which　cannot　be　considered　by　the　standard　UDT.　When　the　residual　charges　are　removed　after　the　gap　breakdown,　the　continuous　breakdown　and　withstand　phenomenon　is　disappeared,　and　the　50%　impulse　breakdown　voltage　U50　is　decreased　under　different　gap　distances,　resting　times,　and　initial　voltages.　The　effect　of　the　residual　charges　is　strengthened　with　the　decrease　in　the　gap　distance.　When　the　breakdown　path　length　is　close　to　30　cm　in　the　air　insulation　gap　and　the　hybrid　gas-solid　insulation　gap,　the　effect　of　residual　charges　is　significant.　The　modified　UDT　method　is　recommended　when　residual　charges　are　present　during　impulse　testing,　which　can　be　indicated　by　the　number　of　tests.　©　1994-2012　IEEE.