Abstract: In the present paper, a water-cooled copper anode was designed. The radial distribution of arc column that after plasma arc penetrated the work-pieces was measured. The effects of welding current and ambient pressure on plasma penetrating arc pressure was studied. The experiment results refer that arc pressure of central area of arc column is maximum, which decreases rapidly along the radial from the center to the edge of arc column. The arc pressure increases with the increasing welding current in the same ambient pressure. Within a certain range of pressure, the arc pressure increases significantly with the deceasing ambient pressure in the same welding current. The change of ambient pressure has a more significant influence on arc pressure than the change of welding current.