Abstract: The mechanical properties and welding metallurgy laws of deposited metal of HS-80 welding wire by laserMAG hybrid welding and MAG welding were studied. The results showed that the yield strength, tensile strength and impact work of the deposited metal by laser-MAG hybrid welding were all enhanced observably compared with those by MAG welding, and the microstructure was finer. Meanwhile the alloying element transition coefficient of laser-MAG hybrid welding was increased. In the laser-MAG hybrid welding process, the weld puddle cooled quickly at the high welding speed and the laser beam made the weld puddle flow acutely. These two technology factors were the main reasons of grain refinement. Moreover the content increasing of some elements such as Ti and Mo, which can make grain finer, was another reason of grain refinement. The grain refinement of the microstructure and the content of alloying elements increasing due to the improving of alloying element transition coefficient were the main reasons that enhanced the toughness and mechanical strength of deposited metal by laser-MAG hybrid welding.