The aerostatic bearing is one of the basic core techniques in the ultra-precision engineering

and the air-film vibration is one of the main factor affecting the manufacturing precision.A capacitive testing method for air-film thickness of aerostatic bearing is proposed

which takes the working surfaces of both the aerostatic reducer and the experiment table as two plates of the capacitive sensor.The capacitance greatly varies with the air-film thickness

thus the air-film thickness can be calculated by measuring the capacitance between them.Meanwhile

mathematical models concerning the capacitance and the air-film thickness of different concave reducer are established.In the experiments

the air-film thickness is measured by both the capacitance meter and the inductance micrometer simultaneously

and the results show that the error between two measuring values is 0.42 μm.It offers a new method for measuring the air-film thickness of the aerostatic bearing.