Abstract: 5754 aluminum alloy with thickness of 10 mm was welded by gas tungsten arc welding (GTAW) and friction stir welding (FSW) using a double-sided synchronization welding method. The fatigue property of welded joints at stress amplitudes of 162, 135, 117, 108,99 MPa was compared and studied, and fracture mechanism was analyzed. The results show that the fatigue strength of GTAW joint at given stress amplitudes was obviously larger than that of FSW joint. The fatigue strength eigenvalues at 50% and 95% survival percent of GTAW joint increased by 26.3% and 24.4%, respectively, compared with those of FSW joint, indicating that the fatigue property of GTAW joint was better than that of FSW joint. The fatigue failure mechanism of GTAW and FSW joints was almost the same. The fatigue cracks all initiated at the outer surface of fusion zone of joints. With the decrease of stress amplitude, the proportion of the fatigue crack propagation zone increased. At the same stress amplitude, the proportion of crack propagation zone of GTAW joint was larger than that of FSW joint. The spacing of fatigue striations in GTAW joint was narrower, indicating that the fatigue life of GTAW joint was larger than that of FSW joint.