Based on the basic principle of differential absorption detection and the spectrum scanning technology of ultra-narrow-bandwidth (UNB) laser, a kind of distributed carbon dioxide detection system with high precision was designed. An UNB laser was utilized as light source and a novel structure gas cell was also used in this system. By using the wavelength modulation technique and space division multiple access technique, the interference of other gas and dust was eliminated and the distributed detection of carbon dioxide was achieved. With the spectrum scanning technology of UNB laser, spectra of carbon dioxide near the region of 1 572.66 μm at different pressures were obtained which were also analyzed. Finally the experiments indicated that the minimum detectable carbon dioxide is 0.005% and the measurement relative error is less then 3%. The system dynamic response time is less than 8 s by filling a volume of carbon dioxide gas into the gas cell gradually.