Abstract: Weld penetration and wire melting speed of AC PMIG welding not only have relationship with welding current but also with electrode negative ratio. When electrode negative ratio is zero,which is using MIG welding with DC and welding wire being positive polarity, weld penetration is maximum,wire melting speed and deposition rate are minimum; as electrode negative ratio increases weld penetration decreases, at the same time, wire melting speed and deposition rate increase. When welding aluminum alloys sheet with AC PMIG welding, shallow weld penetration can form at the same time of forming high deposition rate by adjusting welding current and electrode negative ratio, which can enhance welding speed,avoid having problems of burn-through and beam sinking, arid stabilize welding quality.