Abstract: The narrow-gap TIG welding with magnetic control system was used to weld the Ti-6Al-4V alloy of 56 mm in thickness. The mechanical properties of weld bead were tested including tensile strength,impact toughness,and hardness. The results shows that the tensile strength value is higher than that of the filler metal due to the meshing strengthened effect. The stress distribution along the through-thickness direction of the joint determines the highest tensile strength and toughness value in the area nearby the welding center line. The welding stress between surface layer and interlayer makes the tensile strength and toughness value decreased. The surface layer has the medium value without welding stress. The highest hardness value appears in the fusion line at the same position on depth because of the acicular α'.