Wind velocity in different barometric pressure and characteristics of the flow field at the vent port of air knife, designed by Institute of Optics and Electronics, Chinese Academy of Sciences, driven by compressed gas were calibrated and analyzed by using a IFA-300 hot-wire anemometer. The results show that wind velocity has a good liner relation with barometric pressure; the larger the pressure is, the greater the velocity is; and the uniformity and stability of flow field at the vent port are related to the location of flow field. In the centre of the flow field, the velocity of flow field was the largest, and the instability was the lowest, its value was close to 2%. On the edge of the flow field, the velocity of flow field was the lowest, and the instability was the largest, its value approximately equaled 28%.