Based on the theory of six-temperature model rate equation a theoretical model on calculating the kinetic characteristics of a grating-tuned TEA CO2 laser is given. As an illustration, the output characteristics of a grating-tuned TEA CO2 laser is calculated out by this theory. In the calculation, a grating with a brazing angle 30° and 120 grooves per millimeter is used. The laser is assumed to be of an active volume 0.9 litter and total gas pressure 61.3 kPa under temperature 300 K. By numerical calculation, the following results are obtained