Abstract: The beam quality of high-power Slab CO₂ laser was measured using LASERSCOPE UFF100 from the aspects of the raw beam and focal beam.The measurement experiments had been done before and after the laser beam passing through the flying optics.And the beam quality of focal beam and focal shift were measured.The measurement results show that the M² factor of focal beam is about 1.1,its beam transverse intensity profile is approaching the ideal Gauss profile,the laser beam can propagate a long way without divergence,the focal beam waist radius is 83 μm when the focal length is 190.5 mm,and the focal shift is about 1 mm in the range of processing (x:0~3 m).