Foil hydrodynamic air bearing is a kind of self-acting hydrodynamic gas bearing which the foil is used for elastic support. Because of its superior dynamic performance, it is widely used in high-speed turbine machinery, high-precision machine tools, aviation, aerospace, national defense and other high-end equipment fields. The foil hydrodynamic air bearing uses the air as the lubricating medium, according to the principle of dynamic pressure lubrication, a certain relative velocity should be reached between the journal and the bearing, so that the dynamic pressure film formed can overcome the radial force of the rotor and make the journal and bearing separate from the mechanical contact, that is, the rotational speed should reach the takeoff velocity of the foil hydrodynamic air bearing. In order to reduce the mechanical contact time between journal and bearing, determine the acceleration time of the motor and accurately measure its takeoff velocity, which has important engineering significance. A method to determine the takeoff speed of foil hydrodynamic air bearing by evaluating the vibration characteristics is proposed.The analysed result shows that accords with the actual result, which verifies the accuracy of the theoretical calculation method and is of great significance to the engineering application of air bearing.