A total output power of 25.5W was achieved after optimizing the transmissivity of the output mirror and the design of the output window in the middle infrared and long infrared dual-band (3～5 μm & 8～12 μm) laser driving by two glow discharge tubes. Power in either single band is greater than 10W. The transverse mode of DF and CO2 laser beam in the middle and long infrared band is TEM00 and TEM20, respectively. An output power of 15.4W was obtained for TEM00 fundamental mode selected with a Φ8mm diaphragm. The dual-band laser can work as light source for research of dual-band or multi-band infrared detector arrays and the related systems.