Abstract: Based on a novel main circuit topology of ultrafast-convert power supply,variable polarity current with the ultrafast current rate of rise and fall was achieved,and the arc behavior of high-frequency variable-polarity tungsten inert-gas welding for aluminum alloy was investigated.The experimental results show that with the increase of current frequency,the cleaning action of ultrafast-convert high-frequency variable-polarity arc for surface oxide is significantly enhanced,arc plasma has an obvious pinch effect,arc voltage and arc resistance increase respectively,but arc blow-effect is also enhanced.Increasing the current frequency and decreasing negative polarity current amplitude and its duration in certain ranges can improve weld penetration and reduce the electrode consumption.It is beneficial to improve weld quality and efficiency for aluminum alloys.