As the main greenhouse gases in the atmosphere, CO2 takes global warming factor up to 60%, leading to a serious impact on the global ecosystem and social development. Therefore, it is necessary to carry out the monitoring of CO2 . Based on the principle of tunable diode laser absorption spectroscopy(TDLAS), a room-temperature DFB laser was used as an optical source, and an absorption line of CO2 near 2004 nm was obtained. The CO2 concentration can be calculated via the Beer-Lambert law. Meanwhile, in order to prove the accuracy of the result, ecological flux standard instrument is used as the reference. The results show that both measurement accuracy is considerable, up to 0.2 ppm. The exploration of the research can provide a basis for instrument miniaturization and a long time monitoring of the CO2.