Variable　polarity　plasma　arc　welding　process　is　an　important　method　for　welding　aluminum　alloy.　Experimental　results　show　that　in　addition　to　current　and　welding　speed,　gas　flow　rate,　shrinkage　of　tungsten　and　the　height　of　the　nozzle　are　very　important　parameters　which　influence　weld　characteristics.　The　surface　Gauss　heat　source　and　the　cylinder　heat　source　were　selected　to　simulate　the　welding　temperature　field.　Through　a　lot　of　experiments,　the　effect　of　main　process　parameters　on　variable　polarity　plasma　arc　welding　was　analyzed.　By　finite　element　analysis　method,　the　relation　between　the　heat　source　model　and　practical　process　parameters　was　established,　and　through　linear　regression　analysis　method　mathematical　formula　was　set　up.