Abstract: In this paper，the object in the sound field is studied，and the acoustic radiation pressure equation

is theoretically derived both in the travelling wave and the standing wave. The concept of the critical suspension

density is introduced into the standing wave sound field，which should be used as a criterion for suspension in a

nonlinear sound field. At the same time，the maximum range of Resonant cavity's movement speed is given. Furthermore，

by the combination of numerical computations and experimental results，the influence of the density and the

size of the sample in the standing wave sound field，the shape of the emitting surface and the reflecting surface，the

distance between these two surface，and the size of the reflecting surface on the suspension stability are investigated.

It is found that when the size and the density of the object are determined，adjusting the length of the resonant cavity

and increasing the sound pressure at the antinode are effective means to improve the acoustic suspension stability.

Key words: standing wave sound field, suspension, stability, sound pressure