Laser welding is the welding of laser beams generated by high-power coherent monochromatic photon streams as heat sources. Such welding methods usually include continuous power laser welding and pulsed power laser welding. The advantage of laser welding is that it does not need to be carried out in vacuum. The drawback is that the penetration is not as strong as that of electron beam welding. Accurate energy control can be achieved during laser welding, and precision micro devices can be welded. It can be applied to many metals, especially the welding of refractory metals and dissimilar metals. The generation of laser: the beam with the same wavelength, frequency and direction produced after the material is stimulated. Characteristics of laser: good monochromatic, good direction, high energy density, laser through transmission or reflection mirror focusing, can get a diameter less than 0.01mm, power density up to 1013W/cm2 of energy beam, can be used as welding, cutting, drilling and surface treatment of heat source. The materials produced by laser are solid, semiconductor, liquid, gas and so on, and the main industrial processes such as welding and cutting are yttrium aluminum garnet (YAG) solid laser and CO2 gas laser. The main advantages of laser welding are: (1) the laser can be flexed through optical fiber, prism and other optical methods. It is suitable for the welding of the parts which are difficult to reach by the micro parts and other welding methods, and can also be welded through transparent materials. (2) high energy density, high speed welding, heat affected zone and welding distortion are very small, especially suitable for welding of heat sensitive materials. (3) the laser is not affected by electromagnetic field, does not produce X rays, and does not need vacuum protection. It can be used for welding large structures. (4) the insulation conductor can be directly welded without having to strip the insulating layer in advance, and the dissimilar material with different physical properties can also be welded. The main disadvantages of laser welding are: expensive equipment, low energy conversion rate (5% ~ 20%), high requirements for welding, assembly and positioning of welding parts. At present, it is mainly used in the welding of micro devices in the electronic industry and instrument industry, as well as the welding of silicon steel sheet and galvanized steel plate.