For the operation of a fluidized bed, solid particle size distribution is related to fluid dynamic behaviors, heat transfer efficiency, combustion efficiency, and desulfurization performance. Measurement of pressure fluctuations has a great advantage for detecting fluidization and combustion conditions, due to its flexible adaption to any operating conditions. In this study, the measurement and analysis of pressure fluctuations in the inlet of a wind cap of fluidized beds were carried out, to investigate the effects of particle size distribution on the gas-solid fluidization behaviors. Pressure fluctuations in the inlet of central wind cap were measured at different primary air velocities in cold circulating fluidized beds with different particle size distributions. In order to obtain the corresponding characteristic parameters, pressure fluctuations were analyzed by the methods including standard deviation, power spectral density estimation, wavelet analysis, and homogeneous index. Based on these characteristic parameters, the effects of particle size distribution on the gas-solid fluidization behaviors in fluidized beds were systematically analyzed. Variations of characteristic parameters of pressure fluctuations were found to be related to the variations of the gas-solid fluidization behaviors, which were caused by changes in particle size distribution or particle sizes. The results of this study indicate that the proposed method is practical, and the research achievements can be used as a theoretical basis for the condition monitoring of particle size distribution or the detection of agglomeration in fluidized beds based on pressure fluctuations in wind caps.