Abstract: Experiment of joining 6061 aluminum alloy and 304 stainless steel plate by molten-brazing operating at pulse-on-pulse welding mode was carried out and lap joints were obtained. The arc shape and welding current as well as voltage was acquired by high speed camera and electric signal acquisition synchronous system. The effect of the action mode of arc(inclination angle of torch and position of arc)on the weld formationand mechanical properties of the joint was conducted.The result showed that different action modes of arc actually had significant influence on the arc shape, weld formation and mechanical properties of the joint.When the anteversion angle is 20°and the heeling angle is 0°, the weld formation is sensitive to the position of arc. While with the anteversion angle of 20°and heeling angle of 0°, the weld formation is insensitive to the position of arc. Under the former condition, when L is -1 mm, 0 mm, 1 mm, the joint of aluminum and stainless steel has higher strength while under the later condition, the joint of aluminum and stainless steel has higher strength when L is 0 mm and 1 mm. The position the arc performs is the key factor to the shear strength of the joint and it also has effect on the thickness of the interface layer. The study of effect of the action way of arc on weld forming and mechanical properties helps us make effective control of the heat distribution in the process of joining aluminum and steel.