Abstract: The physical mechanism of interaction between laser beam and arc is a difficulty for the laser-arc hybrid welding technology.During the process of laser-arc hybrid welding,arc is fixed and compressed by laser-induced keyhole,because laser energy will be absorbed and defocused by arc,it directly effect the stable forming of keyhole.Therefore,the investigation of absorption and transmission characteristics of laser in the arc is very important for analyzing hybrid welding mechanism and selecting welding parameter.In this paper,a new test is developed for quantitative measurement of absorption and defocusing of arc on CO₂ laser.The transparent perspex is employed as samples,the ablation depth and width of samples acted by laser is used for reflecting the loss of laser energy.Using this method,the influence of arc on laser energy under the condition of different welding current and arc location are indicated.