Joining of aluminum-magnesium dissimilar alloys can broaden the application of lightweight structures,so it is of great scientific value and economic benefits. The comparison tests between conventional friction stir welding (FSW) and ultrasonic vibration enhanced friction stir welding (UVeFSW) are conducted,and the experimental results are analyzed. It shows that the exerted ultrasound can broaden the process-parameter window,improve the surface smooth of the weld,reduce the occurrence tendency of defects,optimize the Al/Mg interface structure,homogenize and refine grains,and improve the mechanical properties of the joints. The load tests demonstrate that the exerted ultrasound can lower the load required for welding so that it’s benefit for reducing the equipment volume. The measured temperature illustrates that the ultrasound produces some preheating effect on the weldment.