When the laser power density reaches a certain value, the temperature of the workpiece surface rises rapidly in a short period of time and reaches its boiling point, causing the metal to vaporize and form an elongated hole. When the metal vapor recoil pressure, liquid metal surface tension, gravity, etc. reach a balanced value, the slender hole no longer continues to deepen, and finally forms a hole with stable properties, temperature, and depth. When the small hole is closed, the weld is formed. , to achieve laser self-fusion welding.