Abstract: By instancing externally pressurized spherical gas bearing with inherently compensation, equivalent mathematical model of static stiffness, dynamic stiffness and frequency response function of aerostatic bearing are built. In the presence of mathematic analysis and numerical experiment, the relation between static stiffness, dynamic stiffness and frequency re-sponse function is opened out theoretically. It is indicated that static stiffness in externally pressurized gas bearing at operating point can be acquired by measure amplitude frequency response characteristics of gas film in low frequency. Operating principle of the test apparatus for spherical gas bearing and influence of apparatus’ mechanical modal to test results are introduced. The results show that the new method of static stiffness measure-ment adopted dynamic test technique is correct and feasible. For inherent nonlinear vibration system consist of gas film and loading mass, dynamic stiffness in low frequency is equal to the static stiffness of the bearing at the operating point. On-line automatic testing of bearing static stiffness can be achieved by the new method and testing accuracy and efficiency is increased. After expansion of excitation frequency to the frequency range involved by mechanical system, static stiffness, dynamic stiff-ness and amplitude frequency response characteristics of exter-nally pressurized gas bearing can be obtained at the same time by the new method. It is highly important to the study of stabil-ity and dynamic property of aerostatic bearing and precise shafting, which can be never implemented only by the static testing method of bearing’s stiffness.

Key words: Amplitude frequency response characteristics, Dynamic stiffness, Externally pressurized gas bearing, Static stiffness