Abstract: The fracture process of the GH series superalloy welded joints with argon tungsten arc welding was observed upon scanning electron microscope in-situ tension using the samples obtained from the same fatigue test-pieces.The relations between the fracture features of in-situ tension and tension fatigue behaviors was discussed.The results reveal that the GH alloys welded joint had excellent strength and the fracture strain reaches up to 17.5%,which shows remarkable strain strengthening effect.It has also discovered that the fracture morphology of the welded joints is closely related to the stress state.The cracks initiated at the crystal defections and the grain boundaries and shown the ductile shear fracture under the plane stress state.Those formed at corners of the sample with stress concentration were liable to be failure with brittle transgranular fracture.The results reveal that the co-effect of stress concentration of welding root/toe and the non-uniformity of microstructures in the welded joints would result in strain hardening of fatigue test-pieces,and therefore to induce initial cracks during fatigue.