Abstract: The plasma -TIG coupling arc hybrid welding process was proposed to improve the welding efficiency of mild steel. The stable coupling arc of plasma and TIG is realized under the action of electromagnetic force by designing the intensive torch, and the welding heat source characteristics of the coupling arc have been optimized. The arc shape, weld formation and, mechanical properties are analyzed. The results showed the coupling arc still have good deep penetration welding characteristics. Compared with plasma and TIG welding method, the coupled arc has more reasonable depth-width radio, and has the effect of shock stirring on droplet and welding pool, which promotes grain refinement and reduces the tendency of joint crystallization in fusion zone. One-side welding both sides formation could be achieved by use of the butt welding test with 5 mm thick Q235B steel plates, the weld was smooth without defects and the tensile strength was better than the base metal.