A fluidized bed control algorithm in which the bed mode was identified by the variance of the pressure fluctuation at the free board has been proposed. The control characteristics of the system regulated by the integral, and proportional plus integral corrective algorithms were studied experimentally and theoretically. The results showed that integral action provided the stable behavior for the system with an intensively fluctuating process. The relationships between the pressure fluctuations observed in the bed were examined by spectrum analysis under the condition of packed bed, minimum fluidization, bubbling, and slugging state. Frequency ranging between 1 and 2 Hz was found to be valid for the recognition of the fluidization regimes.