Abstract: In order to study the effect of metal vapor on the arc characteristics of gas metal arc welding (GMAW) under the action of DC longitudinal magnetic field, tungsten-copper composites were made into special tungsten electrode instead of molten electrode to produce copper vapor, which was tested and studied by high speed camera method, spectral temperature measurement method and keyhole detection method. The results show that when copper vapor enters the arc plasma, the arc appears delamination. With the increase of copper vapor content, the outer radius of arc core increases, and the size of the arc core area decreases. When the Cu content is 0%, after the DC magnetic field is applied, the arc shrinks in the cathode and expands in anode with an notable increase in the axial maximum temperature of the arc. The peak value of the arc pressure deviates from the axis, and when the magnetic field intensity B = 0.015 T , the arc pressure shows a bimodal distribution. The distribution of current density is similar to that of arc pressure. With the intervention of copper vapor, the arc in the arc core region shrinks in the cathode and expands in the anode region. While the copper vapor around the arc core shrinks obviously, and the rise of the maximum axial temperature of the arc decreases obviously. At the same time, the copper vapor expands the conductive area of the arc, weakens the circumferential electromagnetic force. The pressure at the arc center decreases, and the distribution of anode current density was flattened.