Tunable Diode Laser Absorption Spectroscopy (TDLAS) is a recently developed laser spectral gas detection technology. Compared with common oxygen sensors such as electrochemical devices and ionic conductive ceramics, TDLAS has the advantages of high selectivity and sensitivity, fast response, on-line measurement and strong anti-background spectral interference ability. Oxygen (O₂) is an important gas in habitable environments and is greatly significant to industrial production and human life, and the detection of O₂ concentration is also widely used in these fields. Based on this, we adopt TDLAS technology to carry out high sensitivity measurements of O₂ in air. Using a semiconductor laser with an output wavelength of 760 nm as the light source, the oxygen concentration in the environment is 20.56% by direct absorption spectroscopy, and the minimum detection limit is 5.53×10^-3. In the wavelength modulation spectroscopy method, the laser wavelength modulation depth is optimized to obtain a complete second harmonic waveform, which can be used to calibrate the oxygen concentration. The SNR of the system is 380.74, and the minimum detection limit is about 540×10^-6. The system realized in this paper has good oxygen detection ability and can be widely used in various fields of oxygen concentration detection.