Abstract: By instruments such as the laser power meter, the beam diagnosis and the fast CCD camera, the effects of the DC TIG arc on the characteristics of a vertically incident CO₂ laser beam were investigated. The experimental results demonstrate that part of the laser beam energy is absorbed by the arc plasma. This absorption increases with the increase of the arc current and the incident laser power, and becomes more evident as the laser beam incident position is closer to the anode. Meanwhile, the laser beam will be defocused, deformed and deviated to the cathode due to the arc refraction. The beam defocusing, deformation and deviation become more obvious with increasing the arc current and the incident laser power, and impinging the laser beam closer to the anode. The combined effect of the absorption and defocusing causes the power density decreases sharply as the beam passes through the arc.