We describe some of the characteristics of intracavity CdTe Q-switch modulation in a CO2 laser, which could be used in a pulsed heterodyne imaging lidar. We analyze the thermal influence of intracavity CdTe crystal on output power stabilization and frequency shift, and conclude that sufficient cooling and temperature control on CdTe modulation is the vital requirement for laser stabilization both in power and frequency. We also calculate the frequency chirps due to CdTe thermal index varieties during individual Q-switch pulse duration. The results show that the chirps may not obviously affect the passive frequency stabilization of the laser. For this laser, Q-switch pulses with peak power 360 W and full width at half maximum (FWHM) of 150 ns at 41.67 KHz are achieved. The experimental results also indicate that the passive frequency stabilization of the laser is better than 1.76×10–8 and power stabilization in the EH11 mode is better than 5% for more than 1 h of operation.