The role of diffusion of the components of the gas mixture is the generation mechanism of a waveguide CO2 laser is analyzed. A method is proposed for reducing the multicomponent problem of linear diffusion with dissipation to a one-component problem. The superposition of relaxation modes for a cylindrical waveguide is considered. The diffusion contribution to the loss of electromagnetic energy is estimated for the case of the field hybrid mode EH11 of a dielectric waveguide. The rapid increase in the loss for a SiO2 waveguide tube and the observation of the filtration properties of the laser in conditions when the diffusion is taken into account are noted.