CO2 concentration has ranked the third of all the trace gas in the earth’s atmosphere and exerts a tremendous influence on greenhouse effect. It mainly comes from human’s daily activities. Detecting atmospheric CO2 concentration has important significance in understanding the periodic changes of CO2 and the inherent law of climate change. Based on tunable diode laser absorption spectroscopy (TDLAS) technology, the absorption line of CO2 near 2004 nm was selected, the open-path atmospheric CO2 was continuously measured by direct absorption processing method. Compared with a hand-held CO2 measurement instrument, their correlation coefficient is 0.8371, and the standard deviation is 7.204 ppm. The results show good consistency between the TDLAS and hand-held CO2 measurement instrument, and the feasibility of experiment system is proved. It provides an important way and a method for the domestic remote sensing of CO2 with laser.