Abstract: The super-long life fatigue properties of 5A06 aluminum alloy TIG welded joint were investigated with a self-made TJU-HJ-I ultrasonic fatigue test device. The results show that the S-N curve descended continuously for the cylindrical-shape base material specimens, cylindrical-shape welded joint specimens and thin plate welded joint specimens after 10⁷ cycles. No obvious turning was found in the S-N curve. The fatigue strength of welded joint in 10⁷ and 10⁷ cycles was just 50%-70% of that of base material. The ultrasonic fatigue fracture morphology of specimens, observed with scanning electron microscope, reveals that the fracture surface in fatigue crack propagation area of base material was flatter than that of welded joint. Dimples existed in the transient rupture zone. However, welding defects like pores and inclusions were found in the welded joint without reinforcement, which significantly degraded the fatigue properties of the welded joint.