Abstract: TIG-MIG hybrid arc is adopted to change deficiencies existing in TIG or MIG welding method.With PID theory, current and voltage of welding power is constantly controlled to achieve TIG and MIG hybrid arc.Thus, property of hybrid arc, transitional form of droplet and influence of different polarity connections to welding seam are studied.Results from above research show that presence of TIG arc made good effect for stability of MIG arc.In the hybrid welding, following minimum voltage rule, TIG arc burns on droplet to heat metal and DCEP has good effect in cleaning oxide film of workpiece.In conclusion, TIG-MIG hybrid arc efficiently reduce welding splash, promote wetting of droplets and formation of welding seam, and realize welding with higher efficiency and better quality.