In order to know the fluidization characteristics in a fluidized bed of binary mixtures, soybean (FK, d(P) = 7.68 mm) and silica gel (SG, d(P) = 1.50 and 3.09 mm), the pressure fluctuations were investigated at lower bed aspect ratios (H/D = 0.56-1.56) by a statistical analysis. The results indicate that the dominant frequency in the bed changes inversely with the static bed height and decreases slightly with the increase of gas velocity provided that the mass fraction of SG is lower. The measuring position along the bed column has an insignificant influence on the dominant frequency; but there exists maximum mean amplitude at a certain position of the bed column, dependent on the fluidizing gas velocity as well as the size of the small particles (SG) added. Generally, by adding small particles into the soybean bed, both the dominant frequency and the mean amplitude of pressure fluctuations could be increased, compared to those in the soybean bed. In addition, at higher gas velocities, slug occurred in the beds of FK and SG3 (d(P) = 3.09 mm), but large bubble and gas-solids eddy in the beds of FK and SG2 (d(P) = 1.50 mm). It was observed that mixing of soybeans could be improved by adding small particles (SG) into the bed.