Abstract: In this artide, the character of combined laser-coaxlsal arc heat source is deeply studled on the basis of understanding hollow tungsten electrode arc. The result states that the combined heat source has a remarkable effect on the enhancement of Welding penetration due to their action each other.As auxilary heat source, the coaxisal arc has more irfluence on augmenting penetnltion depth than the non-coaxisal arc. The variation rule of the welding penetration depth with the combined laser-coaxisal arc is given based on the experiments.