Abstract: To improve the arc pressure and energy density of tungsten insert gas (TIG) welding, a welding method of helium arc was proposed, in which helium was used as the shielding gas. The arc morphology was recorded by using a high speed camera, the arc pressure and current density were measured and calculated at the same time, and compared with that of the conventional TIG arc. The experimental results show that, the cross section diameter of helium arc is significantly less than that of the conventional TIG arc at the same current, the maximum of arc pressure in helium arc is significantly larger than that of TIG arc, and the current density of helium arc is more concentrated than that of conventional TIG arc. The arc was used to ablate a fixed spot on work-piece to clearly show the arc energy transformation of the helium arc and conventional TIG arc. The sizes of the surface of the molten pool and grain of welded joint were analyzed to study the heat transfer. The results show that the width and depth of welded joint by helium arc are larger than those by the traditional TIG arc.