The invention relates to a processing technology for refining weld joint structures in a welding process, in particular to a method and a device for refining weld joint structures by using pulsed magnet fields in the welding process, and belongs to the technical field of welding. The method for refining weld joint structures by using pulsed magnet fields in the welding process includes that welding is performed by using an ordinary gas metal arc welding method, an applied magnetic field is added above a gas metal arc welding pool, mechanical movement and welding gun movement of the magnet fields are synchronous, electric arc and melt drip transition action is controlled by the magnet fields in a welding process, metal melt in the gas metal arc welding pool is forced to move, an electromagnetic stirring effect is produced, and weld joint structures are finally refined in the welding process. According to the method and the device, in the welding process, the weld joint structures are refined, welding defects are reduced, and further the cost is reduced, and the welding quality and the production efficiency are improved.