Quantitative research on energy and material exchange between the land or ocean and the atmosphere, especially the monitoring of carbon dioxide (CO2) exchange flux, play an important role in the study of global carbon cycle and climate change.We developed an open-path CO2 detection system based on direct absorption spectroscopy technology and derivative spectroscopy technology for on-line measurement across an order of km air path. A movable platform was developed capable of detecting atmospheric variations of CO2 in real time with the integrated optical system of transceiver.Allan variance analysis shows the detection limit of the system is 0.08×10-6 at the integration time of 100 s.The feasibility of the method with the second derivative spectrum is verified by using standard gases with different concentrations for the concentration calibration, and the correlation is 0.998. The continuous operation was carried out at Shenzhen Eco-environment Monitoring Station for 1 month, and the detection results have obvious daily variation periodicity.Comparing the data with the Licor7550-CO2 monitor installed at different points nearby, the data change trend is consistent, and the stabilityof the prototype is better.