Optimization of ultrahigh frequency pulsed VP-GTAW (HPVP-GTAW) welding parameters on microhardness for 5A06 aluminum alloy was carried out. Taguchi method was employed to design the experiment. The microhardness of the fusion zone and heat affected zone (HAZ) was taken as indicator, and the characteristic welding current parameters of HPVP-GTAW were taken as factors. The experimental results were analyzed by both the range analysis method and regression analysis method. Results show that the optimal parameters of variable polarity current frequency fL, pulse frequency fH and pulsed current proportional coefficient ψ are 1kHz, 20kHz and 0.6 (high-frequency background current 75A, high-frequency peak current 180A, duty cycle of high-frequency pulse 0.2), respectively. Meanwhile, fL influences on microhardness the most significantly, followed by fH, and the impact extent of ψ on microhardness is the least. The confirmatory experiment shows that the microhardness, tensile strength, percent elongation and ratio of reduction with the obtained optimal parameters are 84.7%、94.3%、80% and 93.4% of those of the base matel, respectively.