Abstract: The spectrums of laser-induced plasma in CO₂ laser welding of 6061 aluminum alloy are measured through PI Pro2500i transient spectrometer.Boltzmann diagrams can be used to calculate the average temperature of laser-induced plasma, which are deduced from Mg Ⅰ spectrums between 200-600 nm.The influence of welding parameters, such as laser power, welding speed, focus position and shielding gas, on laser-induced plasma temperature are investigated separately and the reasons are also discussed.Under the experimental conditions, laser power plays little role on laser-induced plasma temperature (6000 K)when it exceeds the threshold power of laser penetration welding.The effect rule of welding speeds on laser-induced plasma temperature likes inverted U curve.Laserinduced plasma temperature has been increased and then decreased when the flow rate of shielding gas is increased for a given diameter of nozzle.Laser-induced plasma temperature will increase 500-1000 K when adding argon in to helium.