Abstract: The high strength low alloy BWELDY960Q steel was welded by using metal active gas welding assisted by mechanical vibration. The effect of the vibration on weld microstructure and impact toughness at low temperature were studied. The results show that, the vibration can promote acicular ferrite formation in weld metal, and the quantity of acicular ferrite in weld metal was increased. Meanwhile, impact toughness at low temperature can be improved by using vibratory assistance. The upper platform value of impact energy was increased by 7.88% and the ductile-brittle transition temperature was slightly reduced. The impact fractured surface of weld metal was changed from uneven surface to flat and smooth with the decrease of temperature, the ratio of fibrous zone on the fracture surface is gradually reduced, and the area of radiated structure is continuously enlarged. Themorphology of the fracture surface is changed from dimple pattern to cleavage rive pattern.