Abstract: Laser welding has become an advanced method in joining materials with high quality due to its high efficiency and high precision. Multi-physical field issues are involved during laser welding process, such as absorption and reflection of laser energy, melting and evaporation of materials, flow of molten pool, fluctuation of keyhole and etc. Establishment of numerical model to reflect the feature of thermal process, and further quantitative description to elucidate key factors and evolution process affecting the laser welding quality, can provide theoretical support and scientific path for high quality laser welding and manufacturing. From the aspect of welding defects, microstructural evolution and residual stress that influences formation quality and service property of laser welds, this paper elaborates the application and development of numerical simulation technology in fundamental problem research of laser welding.