Abstract: Based on butt welding during Ti-6Al-4V(TC4) titanium alloys plate with the thickness of 1.5mm,microstructure of weld face and properties of welded joint were investigated by ultrasonic frequency pulse gas tungsten arc welding(GTAW).Compared with conventional direct current GTAW process,the experimental results show that ultrasonic frequency pulse current causes the energy concentration with an obvious pinch effect of arc plasma and the increasing escape speed of gas pore.Grain refining and the elimination of gas pore are due to the enhancement of fluid flow by ultrasonic frequency pulse GTAW process for Ti-6Al-4V titanium alloys.The main structure of subcrystal is the basketweave microstructure composed of rod-shaped martensite or the interlaced microstructure composed of both rod-shaped and plate phase.Similarly,ultrasonic frequency pulse GTAW process could also improve the elongation and reduction of area.