Abstract: The temperature field for the conventional TIG welding of fine grain titanium alloy Ti-6Al-4V with different grain sizes is studied by numerical and experimental methods.The results show that the temperature field patterns and the temperature developing histories of fine grain Ti-6Al-4V alloy with different grain sizes are similar.But because of the refinement of base material grain size and the increment of grain boundaries,thermal conductivity and specific heat are both reduced,and the value of specific heat reduced is larger than that of thermal conductivity.So the heat conduction abilities of finer grain titanium alloy are weakened,the isothermal range of fine grained titanium alloys is larger than that of coarse grained titanium alloys,and the further the distances to central line of weld is,the more visible the difference is.The peak temperature of points with same distances to central line in fine grained titanium alloy is higher than that in coarse grained titanium alloy.