According to the real-time and accurate measurement of oxygen concentration in narrow space during flight test，the existing problems of oxygen concentration measurement system used in flight test are analyzed firstly, TDLAS is proposed to measure the oxygen concentration of fuel tank. Secondly, the internal structure of the system is optimized to achieve gas-liquid separation and miniaturization. The final volume is more than ten times smaller than the existing equipment, and the wavelength modulation technology and temperature/pressure compensation algorithm are used to improve the oxygen concentration detection capability of the system in the airborne environment. Finally, the reliability of the system was verified through ground and flight tests. The maximum measurement error is 0.28%, reaching the international advanced level of airborne oxygen concentration measurement, laying the foundation for the subsequent identification of various types of inerting systems.