During the process of laser-arc hybrid welding, the metal vapor from the wire end has great influence on the electron number and the particles in the plasma, which changes the absorption of the laser irradiation and the energy input to workpiece.In this paper, an optical emission spectroscopy system was employed to estimate plasma temperature and the electron number densities distribution. A high speed camera was used to analyze the plasma shape behavior. By using the Beer-Lambert law, the laser absorption rate under different welding mode was calculated. The result shows that the metal vapor from the wire tip lead the electron density increase, and it make the laser energy absorption rates decreased.