A discharge driven two-module small scale continuous wave (CW) DF/HF single line chemical laser applied to atmospheric absorption measurement was built. The structure, running manner, and the performance of the laser were described in detail. With the first order oscillating, first order output Littrow grating dispersion laser cavity, 17 DF lines and 11 HF lines are selected. Most of the single lines’ fundamental mode output exceeds 1 W and stabilizes in 5% scale through the 30 min running time. By altering grating to spherical cavity mirror, 20 W multi-line DF lasing and multi-line HF lasing could be realized with this device, and with an aperture inside the laser cavity to discriminate the higher order transverse modes, 6～8 W multi-line fundamental mode lasing could be obtained.