Abstract: The fatigue property and fracture mechanism of TC4 titanium alloy joint during laser welding was investigated.It was found that the fatigue life of laser weld was longer than that of the base metal under low stress levels.However,the fatigue life of laser weld was shorter than that of the base metal under high stress levels.Fatigue cracks originated in the surface for base metal specimen.In the fatigue crack expansion zone,numerous curving secondary cracks and fatigue striations were found perpendicular to the direction of crack propagation.Fissures at the root of some fatigue striations were also observed.The fatigue cracks of the weld originated in the pores in the weld surface,and numerous secondary cracks were straight and parallel near the fatigue resource.In the fatigue crack propagation area of the weld,small dimples were found in fine-grain zone and became shallow near the columnar crystal.Mass of micro-shear sliding bands and shallow dimples were found in the weld center.The fracture mechanism of the weld was formation of shear sliding bands and rupture.