Abstract: The use of spectroscopic technology for gas measurement is to trace the gas value to the line intensity of the gaseous molecule. This paper introduces the latest research progress of gas spectroscopy measurement technology by the National Institute of Metrology, China. The cavity length stabilization, Pound-Drever-Hall frequency locking, temperature controlling technique. and optical frequency combs are used in the experimental setup of the cavity ring-down spectrometer. The temperature change does not exceed 5 mK in 3 hours, and the vacuum leakage does not exceed 0.013 Pa in 1 hour. The absorption line of CO₂ molecule was measured by the developed experimental device, and the source of uncertainty of the transition line intensity was analyzed and given. The relative standard uncertainty of the evaluation was about 0.08%.