A group of the stainless steel laser welding was performed using continuous wave （CW） laser and pulsed laser. During the welding process the laser induced plasma behavior was recorded by high-speed video camera, while the plasma spectrum was acquired by the spectrometer. The plasma temperature was calculated based on the spectroscopic analysis of the optical emission and the results show that different output mode of laser source led to big difference of plasma temperature. The high-speed video images showed that the plasma was very steady and kept certain strength in CW laser welding, while the plasma erupted a little later after the laser peak arising during the pulsed laser welding. During a period of time about 2 ms just after the laser peak arising during the pulsed laser welding, much more laser energy reached the workpiece. This made the workpicce fully penetrated with a lower average power.
