Compared with traditional welding methods, high-power laser welding is characterized by high efficiency and good welding quality, especially in the welding process of thick plates. However, it was found out in recent researches when the laser power increased to a certain level, the welding penetration won’t get deeper any longer due to the absorption,refraction and the scattering effect of the plasma plume. That is generated by the evaporation of metal, and to prevent the laser beam from entering the keyhole. Welding under subatmospheric pressure is regard as an effective method and has an impressive promotion on both welding penetration and porosity defects. The development of the high-power laser welding under subatmospheric pressure, as well as some relevant issues are summarized according to recent researches.