This study presents an absorption-area-based method for the measurement of gas flow velocity using diode laser absorption spectroscopy. In the proposed method, the gas flow velocity is determined using the area difference between the absorption lines. To verify the proposed method, flow velocity measurements are conducted for test conditions with a velocity range of 5–30 m/s in a low-speed wind tunnel, and the results are compared with those of the conventional method using the Doppler-shifted peak. Oxygen in the air is selected as the target gas. By comparing the flow velocity measurement results of the conventional method and the proposed area-based method, it is confirmed that the measurement precision is improved when the proposed area-based method is used. Moreover, the measurement accuracy of the proposed area-based method is significantly improved at a relatively low-speed range of 5–10 m/s compared to the conventional method.