Takes the heat source using the plasma arc the welding method.The gas has the dissociation by the electric-arc heating, when high speed through water cooling spray nozzle receives the compression, increases the energy density and the degree of dissociation, forms the plasma arc.Its stability, the calorific capacity and the temperature all are higher than the common electric arc, thus has the big melt thoroughly strength and the welding speed.Forms the welded joint the way to have melts thoroughly the type and the perforation type two kinds.The preceding form plasma arc only melts thoroughly the parent metal, forms the welding molten bath, uses in 0.8~3 millimeter thick plate welding; The latter form plasma arc only melts puts on the plate, forms the key hole shape the molten bath, uses in 3~12 millimeter thick plate weldings.In addition, but also has the undercurrent micro to tie the plasma arc welding, suits specially in 0.02~1.5 millimeter thin steel plate welding.