Variable　polarity　pulsed　MIG　welding　of　thin　sheet　aluminum　alloy　is　realized　by　full　bridge　bidirectional　high　voltage　arc　stabilizing　method,　and　the　influences　of　voltage　amplitude　of　high　voltage　arc　stabilizing　pulse,　pulse　duration,　pulse　triggering　time　and　background　current　on　cross　zero　stability　are　also　investigated.　When　small　background　current　crosses　zero,　the　influence　of　arc　stabilizing　pulse　voltage　on　cross　zero　stabilities　is　more　than　that　of　background　current.　The　rise　rate　of　arc　stabilizing　pulse　voltage　which　influences　the　cross　zero　stability　has　a　critical　span,　in　which　the　arc　is　unstable　when　arc　current　crosses　zero.　Estimating　the　cross　zero　stability　of　VP　PMIG　through　calculating　the　rate　of　arc　stabilizing　pulse　voltage,　it　can　offer　an　efficacious　and　credible　warranty　to　the　reignition　of　the　cross　zero　welding　arc　of　aluminum　alloy　VP　PMIG.