Abstract: In this paper,by combining the characteristics of electrochemical reaction with that of the engineering aspects of the fluidized bed, the voltage fluctuation phenomena have been theoretically studied and a new mechanism has been put forward. The main point of the mechanism is that, for a given reaction system, the polarity state on the solid particles surface changes with the degree of fluidized bed expansion. For a certain fluidized bed electrochemical reactor there must be an optimal degree of bed expansion.at which the highest superficial current and space-time yield can be obtained. An experimental apparatus for studying the voltage fluctuations is presented with a side-by-side type reactor, silver particles and AgNO3 solution as the electrolyte. The voltage fluctuation values can be measured with a composite probe and an A/D converter as programmed by computer. The power spectra of voltage fluctuation can be calculated with Fast Fourier Transformation.