In order to meet the application requirements of airborne laser differential absorption lidar for small and lightweight light sources, a compact pulsed CO₂ laser is developed with automatic wavelength tuning. First, the aperture matching relationship between an RF waveguide intracavity beam and a free space optical chopper beam was studied, and a beam conversion system was designed with real focus on the intracavity. The influence of the chopper aperture on a laser pulse waveform was verified experimentally. Secondly, the wavelength tuning characteristics of CO₂ laser were studied, and the diffraction angle difference between adjacent laser spectral lines was analyzed. Tunable operation in the CO₂ laser was realized using a high-precision electric turntable and metal blazed grating. Finally, the integration of a compact automatic tuning pulsed CO₂ laser was completed using small lightweight modules. Experimental results indicate that the laser operates stably at 1 kHz with a pulse width of 350 ns and a peak power of 3.7 kW. There are 30 lines within 9.2~10.7 μm waveband. The total weight of the laser is 18 kg. It provides a miniaturized detection light source for airborne laser differential absorption lidar.