Objective A large amount of plasma / metal vapor is generated during the laser welding of titanium alloy. The plasma / metal vapor contains a large amount of welding information. By studying the relationship between the information and the welding state the real-time feedback and adjustment of the welding state can be realized which provides the basis for welding automation. Methods Taking TC4 titanium alloy as the experimental object a laser scanning welding process was added. The morphology and the rule of spectral variation of the metal vapor during the welding process were investigated by means of high-speed camera and spectral acquisition. Results The experimental results showed that the plasma / metal vapor swing amplitude decreased the keyhole effect weakened and the welding stability was improved after the scanning was added during spot welding. In mobile welding without scanning the increase in laser power and the slowing down of welding speed significantly increased the spectral intensity. However after the addition of scanning the increase in laser power and the slowing down of welding speed had little influence on the spectral intensity and the spectral intensity wasn?? t significantly improved. Conclusion The addition of scanning in spot welding can reduce the swing amplitude of plasma and improve the stability of welding. When scanning is added to the process of mobile welding the spectral intensity can be suppressed and the stability of welding can be improved.