Abstract: The sound field on any plane near a sound source can be regarded as the superposition of a plane propagation wave and an evanescent wave. Taking a circular piston as an example, the distributions of the propagation wave and the evanescent wave of the radiated sound field are obtained by using the angular spectrum method. The sound pressure on the sound axis of a circular piston is calculated by using numerical analysis method, and the corresponding near-field sound pressure distribution curve is obtained. The dividing position between near field and far field obtained by the angular spectrum method is consistent with the one obtained by the point source combination method. By comparing the sound pressure distribution curves of the pistons with different radii at different radiation frequencies, the variation law of near-field sound pressure is obtained. The radiation field of the stepped circular plate should be equal to the one of the corresponding circular piston theoretically. In this paper, the axial sound pressure of the designed stepped circular plate is measured, and the experimental results are basically in agreement with the theoretical results.