To overcome some disadvantages of traditional methods to measure the oxygen concentration, the tunable diode laser absorption spectroscopy combined with the phase-lock amplifier is studied. By tuning the drive current of the laser diode (LD) to change the output wavelength, one or more absorption peaks of the oxygen will be scanned. And then the phase lock technique will be used to analyze the harmonic signal of the absorption spectroscopy. This method combines the high power, good monochrome, wavelength easily tuned with the drive current and the advantage of phase-lock amplifier to improve the signal and noise ratio and the measure precision. Through the measurements of some different concentration oxygens, the correlation coefficient of the result is 0.99 and the detection limit is 1142.86 mg/m3, moreover the method has the good stability and anti-interference feature.