Abstract: The effect of microstructure on fracture behavior and mechanism of Ti-6Al-4V electron beam welded joint was investigated by means of scanning electron microscopy,transmission electron microscopy,and microhardness.The results indicated that the weld microstructure were composed of coarse needle α+β phases and martensite of multi-direcitonal short needle morphology.The weld coarse grain with size of 200-350 μm,and the microhardness was 536 HV.High brittleness of the microtructure makes it easy to fracture in the region.The uneven distribution of the partial micropores located at the interior of the specimen acting as crack initiation sites lead to non-linear branch propagating path.The α+β interlaced structure results in fracture near α/β interface because of the different thermal expansion coefficient.The existence of stacking fault structure caused pile-up of dislocation to produce micropores as new fracture initiation sites.