An acousto-optic Q-switched CO2 laser with a quasi-waveguide cavity has been developed. The maximum peak powers of the laser of 1.1 kW and 2.05 kW have been obtained for the cavity lengths of 515 mm and 700 mm respectively. The minimum pulse width was 100 ns, and the pulse repitition rate was 0～300 kHz. The calculated results of rate equations of the laser were approximately consistent with the experimental values.