Pharmaceutical vial’s oxygen concentration detection based on wavelength modulation spectroscopy (WMS) was conducted on a single, short optical path in the open. The oxygen absorption lines at 760.885 nm (13 142.58 cm-1 ) were chosen- and the system parameters were optimized. Then, data processing method and steps were explained, such as real-time background deduction and real-time spectrum correction. Seven samples of the different oxygen concentrations were tested, and the corresponding second harmonic signals were obtained. Finally, the linear regression equations were established between the concentration and the peak height(C—H), the peak area at half maximum(C—A). The experimental results indicated that the fitting coefficients of two methods were 0.996 6 and 0.997 8, respectively, and the latter was increased by 0.12 % than the former. Prediction accuracy of the model was evaluated by fully interactive authentication method and the results indicated that the root mean square errors of prediction (RMSEP) were 0.003 1 and 0.002 0, respectively, and the latter was reduced by 37.69% than the former. The 2f signal of sample ( 4%) were severally measured for 20 times by the two methods in different time and the results indicated that standard deviations were 0.002 2 and 0.001 6, respectively, and the latter was reduced by 27.3% than the former. Meanwhile, the resolutions were 0.198% and 0.097%, respectively, and the latter was increased by 51% than the former. The system is feasible to measure the pharmaceutical vial’s oxygen concentration, and the accuracy and stability of the system can be improved by the C—A method.