The common design of high power CO<sub>2</sub> lasers is based on the fast gas flow to remove the heat produced in the
electrically gas discharge plasma, in this paper, we shall discussed the parameter design consideration for the high power
RF excited diffusively cooled slab waveguide laser, which including the RF power deposition density and RF discharge
longitudinal uniformity. Besides, a kilowatts RF excited diffusively cooled all-metal slab waveguide CO<sub>2</sub> laser is presented, from this type of structure; a laser power output of 1475w was obtained and a maximum efficiency of over 13% was achieved.