By analyzing the ultra fine atmospheric CO₂ absorption spectrum, the infrared laser wavelength can be choiced for detecting the atmosphere CO₂ concentration. It can provide the basis for a wide spectrum infrared lidar. The spectrum of wide spectrum infrared laser is much wider than the differential absorption lidar, and it has no use for high frequency locking technology. Also, this technology can avoid differential absorption lidar measurement error by the on wavelength shift. By analyzing the water vapour absorption spectrum, super luminescent diode (SLED)′s luminescent spectrum and InGaAs infrared detector′s response spectrum, the wide spectrum laser center wavelength is 1572 nm and the spectral range is 1568~1575 nm in theory. By the experimental laser source,the results show that the center wavelength is 1571 nm, the spectral range is 1564~1578 nm, the output power is 0.01 mW. This laser can avoid the influence by the water vapour absorption, and it is simple, low cost and easy to build. It can help for the development of the atmosphere CO₂ concentration detecting by the wide spectrum infrared lidar.