A new kind of a radio frequency (RF) excited diffusively cooled gain slab waveguide CO2 laser was presented. In this type of laser,to improve the quality of output laser beam and enhance the mode coupling between multi-waveguide sub-channels, grooves were made on the top electrode to form a list of parallel sub-electrodes, which can produce the periodically gain distribution along the transverse direction of waveguide. A phase-shifted totally reflecting copper mirror with periodically grooves on the surface was employed and the interference superposition of far-field sub-laser-beams was obtained.The near-field and spatially compressed single peak far-field intensity distributions of output laser beam were studied at pressures of 10.0 kPa and 10.7 kPa, respectively.