The fluidization behavior of Geldart D particles in the deep fluidized bed was systematically investigated through the pressure fluctuation measurement, high-speed camera, and intrusive acoustic emission (AE) detection method. Results displayed that, both in the three-dimensional (3D) fluidized bed and the pseudo-2D fluidized bed, with the increase of gas velocity, the deep fluidized bed of Geldart D particles would experience three different fluidization regimes: the slow bubble regime, slugging regime, and the turbulent regime. The consistency of regimes indicated the rationality of studying the fluidization behavior in the pseudo-2D fluidized bed. In addition, in the slow bubble regime, due to the wall effect, stratified fluidization was observed in the pseudo-2D fluidized bed but not in the 3D fluidized bed. In the turbulent regime, the gas bypassing appeared in the center of both pseudo-2D and 3D fluidized beds.