Abstract: The weld formation characteristics in the hybrid ultra-high frequency pulse variable polarity gas tungsten arc welding (HPVP-GTAW) of 2219-T87 high strength aluminum alloy was investigated. The experimental results show that,under the condition of keeping the RMS of positive current approximately consistent (with permissible variation of ±5 A),welding with ultra-high frequency pulse square-wave current increased the ratio of weld depth to width by more than 20%,compared with the traditional variable polarity GTAW process. Pulse current frequency significantly affected the weld formation. Increasing the pulse current amplitude and decreasing the pulse current duty cycle within a certain range can remarkably enhance the weld penetration. The ratio of weld depth to width increased by more than 75% when the pulse current was 100 A and the pulse current duty cycle was 20%.