Laser beam welding has emerged as one of the most promising connection techniques for lightweight equipment fabricated by magnesium alloys due to the less deformation, narrow heat-affected zone, and excellent welding efficiency. However, a variety of porosity defects are commonly found in the laser welded joints. The causes of laser-welded pores are complicated. And the number, size and distribution characteristics of porosity lead to reduction in mechanical properties of magnesium alloy joints, thus seriously affects the reliable applications of magnesium alloy lightweight equipment. This paper reviews the mechanism of pores formation in the microstructure of laser welding joints of magnesium alloys, discusses the influence of porosity on mechanical properties. The pore manipulation is proposed. The key basic research and applications of LBW-ed magnesium alloys are pointed out. This review may provide valuable insights for the development of joining and manufacturing technology of magnesium alloy lightweight parts in automotive and aerospace fields.