Method for welding thick copper plate by fiber laser

The invention is suitable for the field of a laser welding process, and provides a method for welding a thick copper plate by a fiber laser. The method comprises the following steps of spraying a welding line of the thick copper plate with a light absorbing coating layer, and welding the welding line, which is sprayed with the light absorbing coating layer, of the thick copper plate by focused laser emitted from the fiber laser, wherein the coating of the light absorbing coating layer comprises light absorbing coating and water-based resin; the light absorbing coating consists of the following components in mass percent: 50-60 percent of ZnO submicron particulates, 20-25 percent of Al2O3 submicron particulates, 20-25 percent of TiO2 submicron particulates; the mass percent sum of all the components is 100 percent. By preinstalling a layer of self-developed light absorbing coating on the surface of the thick copper plate, the energy utilization rate when the thick copper plate is welded by the fiber laser is greatly increased, the welding penetration is increased, and the welding efficiency is increased; ceramic clinker of which the proportion is less than that of copper alloy covers the surface of a weld pool, and therefore the weld pool can be effectively prevented from being oxidized; without welding shield gas, the higher welding line quality can also be obtained.