The standard deviation of pressure fluctuations is always as a benchmark to characterize fluidized bed, especially in identifying the transition velocities and flow regimes. In this study, the energy of power spectral density function (PSDF) was proved to be a new alternative tool to effectively analyse the pressure fluctuations. Also, the wavelet analysis was significant to deal with the signals in multi-resolution decomposition and in identification of transition velocities and flow regimes. The results from the normalized energy of PSDF and wavelet analysis are in good agreement with the standard deviation analysis.