In designing the kW order TEM00 mode continuous wave laser unit, a quasi-sealed-off and multi-folded resonator that has the good transverse mode selection ability was developed. In order to insure the mode volume matches with the discharge volume well, the negative thennal lensing effect was taken into account, resulting in the stable output laser whose power is high enough. Based on the forgoing design, a mechanical chopper Q-switched CO: pulse laser was developed then. The resonator parameters were adjusted, including the calculation of the positive thermal lensing effect of the high power laser windows. At last, a Q-switched CO2 laser pulse with the highest average output power of 800 and TEMoo mode was obtained.