The technology of the directly laser absorption spectroscopy for CO2 concentration measurement is described. A tunable diode laser near 2 μm is used as optical source. The multi-pass absorption technology combined with optical fiber transmission technique is improved for this method. Seventeen absorption lines of CO2 are observed and the corresponding spectral parameters (i.e. positions, the transition of absorption band) are presented. The absorption line of CO2 molecule near 2008 nm is recorded in different pressures, from which calibration factor of experimental system at low pressures is retrieved. A CO2 molecule concentration of (2.754±0.145)×1016 cm-3 in the sample gas is also achieved. The resulting accuracy in the retrieved values of gas concentration could be strongly limited by an accuracy of a vacuum gauge using in our measurements. It is proved that this spectral measurement method is an attractive tool for gas concentration monitoring application and isotope abundance analysis.