The　discharge　characteristic　and　plasma　parameters　of　electrical　explosion　of　aluminum　thin　wire　were　studied　by　framing　camera　and　spectrograph.　The　experiments　were　carried　out　under　several　different　discharge　voltages　with　aluminum　wires　of　40　μm　and　100　μm　in　diameter.　The　experiments　show　that　there　are　two　types　of　secondary　breakdown　processes　in　the　metal　vapor:　inner　breakdown　and　surface　breakdown.　The　inner　breakdown,　which　generates　a　plasma　with　better　spatial　uniformity　and　symmetry　and　consequently　leads　to　more　steady　and　repeatable　discharge,　takes　place　more　easily　in　thinner　wire　under　the　same　conditions.　The　electron　temperature　and　density　of　the　plasma　have　the　order　of　magnitude　of　104　K　and　1018　cm-3,　respectively.