Mid-infrared spectrum region is the fundamental absorption band of molecules. Tunable diode laser absorption spectroscopy (TDLAS) technology can be applied to detect greenhouse gas sensitively by scanning a single molecular absorption line. A miniaturized system based on the combination of direct absorption method and a 2704 nm band laser is presented, which is utilized to monitor carbon dioxide. Also, the digital signal processor (DSP) data acquisition system can be applied to acquire and process the absorption signal, as well as to revise the concentration according to the environment temperature and altitude. In order to eliminate the shift of wavelength and ensure the detection accuracy, the wavelength locking module is used and finally a SD card is used for data storage. The system is powered by a battery, the response time is 1.6 s and the detection limit is 5×10-7. It takes a long time to test the system, which ensures its stability and feasibility.