Abstract: High pressure environment has a great negative effect on welding process.Weld width, penetration, reinforcement and Vickers hardness of welded joint were used as the main evaluation indexes in experiment, influence of ambient pressure and pulse frequency on weld formation and properties of ultra-sonic frequency DC pulse TIG joint was analyzed.Research showed that under the same environmental pressure, as pulse frequency increased, weld width decreased and penetration increased.As pulse frequency increased, width and depth of HAZ decreased accordingly, the overall size of HAZ decreased, which showed that ultrasonic frequency DC pulsed TIG had advantage of reducing heat-affected zone and improving quality of welded joint.Weld width and penetration of filler zone decreased with the increase of pulse frequency, the overall change of reinforcement was not big, and influence of pulsed frequency on reinforcement was limited.The overall trend hardness curves of the weld obtained under different pulse frequencies at the same ambient pressure was the same, and hardness decreased from weld to fusion zone, then to heat affected zone and base metal.With the increase of ambient pressure, cooling rate of weld metal increased, and hardness increased with the increase of brittle-hard structure.