Abstract: The mechanical properties and the solidification cracking resistance of the weld could be improved by grain refining. The grain refining method with ultrasonic vibration of workpiece was difficult when the workpiece is clamped down tightly to a rigid fixture or connected to a rigid structure. A new grain refining method with ultrasonic energy was designed, i.e., dipping an ultrasonic probe in the weld pool to stir it at a distance behind the arc. The results show that, this new approach produced effective grain refining in arc welds of 6061Al. Grain refining area increased with the ultrasonic amplitude increasing while the welding speed didn't affect the grain size effectively. Meanwhile, the grain refining of 6061Al welds were achieved with the combination effect of heterogeneous nucleation and dendrite fragmentation.