PURPOSE: To perform welding with free from defects such as blow holes by moving a plasma welding torch after the current value to be applied on the torch attains a prescribed value, decreasing gradually the current value just prior to the end of the movement and extinguishing the arc after the movement of the torch is stopped.

CONSTITUTION: The current value to be applied to a welding torch 14 which generates a plasma jet 13 is gradually increased while the torch 14 is held static toward members 1 to be welded. The torch 14 is moved along the mated parts of the members 1 when the prescribed current value is attained. The current to be applied to the torch 14 is gradually decreased in the position just before the end of the movement. The arc is extinguished upon lapse of a prescribed time after the torch 14 ends moving. Uniform penetration is obtd. by such plasma arc welding method, and the good finish is obtd. without generation of blowhole-like cavities.