A second-order mechanical vibration model is proposed to explain the oscillation phenomena and pressure fluctuations in gas-solid fluidized beds. Experiments were conducted in a 0.1-m ID gas-solid fluidized bed driven by periodic gas pulses with the frequency varying from 0.2 to 10 Hz. Experimental results indicate that the proposed mechanical vibration model, which considers the pressure fluctuation as the results of the response of the fluidized bed to the external excitation forces related to the bubble behavior in the bed, can reasonably explain the pressure fluctuations of the gas-solid fluidized bed. The behavior of pressure fluctuations is correlated with characteristics of both the bed system and excitation forces. (C) 2004 Elsevier B.V. All rights reserved.