With the improvement of laser beam quality and the increasing of laser power output, the percentage of deep penetration laser welding increases gradually in laser processing and welding field. The recent major research achievements of deep penetration laser welding have been summarized, meanwhile, its characteristics and limitations have been discussed as well. And then many important advances have been analyzed and discussed in the field of deep penetration laser welding, such as the research of high power laser, stability of laser welding process, control of laser-induced plasma, auxiliary electromagnetic fields, laser-arc hybrid welding and so on. Finally, the development foreground of deep penetration laser welding in the future is prospected.