Abstract: Ti-6Al-4V alloy was welded by conventional tungsten inert-gas arc welding(TIG) and ultra-sonic pulse TIG welding(U-TIG) respectively.The microstructure of the joint was analyzed by means of optical microscope,scanning electron microscope and X-ray diffraction to study the relationship between the macro-properties and the microstructure of the joint.The results show that U-TIG welding can reduce pores of joint.With the increment of pulse frequency,the microstructure becomes finer and finer and is inclined to equiaxed crystal;while pulse frequency is 45 kHz,the effect of grain refinement is the best.Moreover,the properties of joint by U-TIG welding are improved compared with that of conventional TIG.The tensile fractures of the joints welded by TIG and U-TIG all present the character of quai-cleavage crack,but the cellular dendrite depredation is not observed obviously in U-TIG joint.