Abstract: Particulate fluidization shows a structure of idealized fluidization of complete homogeneity. Aggregative fluidization is characterized by a clear two phase structure,viz., the bubble phase and the emulsion phase. The structure of bed would change at the transition from particulate to aggregative fluidization. In this paper,an optimal algorithm is proposed to compute simultaneously the correlation dimension and the Kolmogorov entropy by the least square method.The change of bed structure corresponding to the transition from particulate to aggregative fluidization is analyzed by using the proposed algorithm from the measured instantaneous pressure fluctuation. Different hydrodynamic behaviors of the two flow regimes are interpreted on different scales. A new criterion is proposed for distinction between particulate and aggregative fluidization.