The laser welding process is accompanied by phenomena of optical radiation, including visible light (metal vapor), laser reflection (laser), and infrared light (heat radiation from the molten pool). These radiated optical signals can reflect the state of welding and whether defects have occurred during the process. By using a photoelectric sensor to convert the optical radiation generated during welding into electrical signals, and analyzing these radiated optical signals through a detection system, the quality of the workpiece welding can be determined, thus achieving the purpose of defect detection and quality monitoring.