Abstract: The electron density of laser, TIG welding arc, and laser+TIG welding arc plasma are measured by the method of Stark Broadened Linewidth. The reason why electric arc enhances laser welding is that the electric arc can dilute the electron density of laser plasma, weaken the ability of laser plasma to absorb and reflect the laser energy, and improve the hot-working efficiency of laser beams. Experiments prove that the combined action of arc and laser beams can obviously improve the weld penetration in welding.