To　enhance　the　reliability　of　aluminum　alloy　welding　quality,　a　novel　Pulsed　Plasma　Gas　Variable　Polarity　Plasma　Arc　Welding　(PPG-VPPAW)　system　is　proposed.　This　system　enables　independent　control　and　rapid　adjustment　of　the　plasma　gas,　allowing　for　flexible　modulation　of　arc　pressure　output　under　constant　thermal　conditions,　thereby　reducing　porosity　and　refining　grain　structure.　The　research　analyzed　the　impact　of　parameters　of　different　plasma　gas　on　arc　characteristics,　welding　porosity,　and　welding　microstructure.　The　results　reveal　that　the　periodic　changes　in　pulsed　plasma　gas　induce　corresponding　variations　in　arc　temperature,　arc　shape,　arc　pressure,　arc　voltage,　and　the　morphology　of　the　weld　pool　keyhole.　The　magnitude　of　the　difference　between　the　base　value　and　peak　value　of　pulsed　plasma　gas　determines　the　extent　of　arc　pressure　fluctuations　and　the　behavior　of　the　backside　keyhole.　The　maximum　oscillation　amplitude　of　the　backside　keyhole　can　reach　up　to　4.5　mm2.　Additionally,　the　oscillation　of　pulsed　plasma　gas　within　the　molten　pool　has　been　demonstrated　to　effectively　reduce　weld　porosity　and　refine　grain　size.　Under　this　process,　the　grain　size　of　the　weld　metal　can　be　reduced　by　up　to　approximately　25%.　Current　work　provides　an　important　direction　for　fabricating　highly　reliable　aluminum　alloy　weldments.