Fluidized reductionFluidized reduction ironmaking process is an important development direction of non-blast furnaceBlast furnace green ironmaking technology. In the paper, the Finex process fluidized bed was taken as the research object, and a three-dimensional bubbling fluidized bedThree-dimensional bubbling fluidized bed model with diameters of 0.189 m was established based on the similarity theory. The effects of the apparent gas velocity and particle size distributionParticle size distribution on the expansion characteristics and pressure fluctuation of a three-dimensional bubbling fluidized bedThree-dimensional bubbling fluidized bed with two and three-particle sizes under full fluidization were studied by cold experimentsCold experiment. The results show that the standard deviation of pressure fluctuation and bed expansion ratio is positively correlated with the apparent gas velocity, and the standard deviation of pressure fluctuation and bed expansion ratio is larger in the fluidized bed with the wider particle size distributionParticle size distribution. The research results can provide a theoretical basis for the parameter design of fluidized reductionFluidized reduction ironmaking process.