The denitrification fluidized bed is an essential component in the nuclear fuel cycle, and the quality of the gas–solid flow characteristics within the bed directly affects the quality of the product. This study utilizes the Computational Particle Fluid Dynamics (CPFD) method, in conjunction with kinetic equations of granular matter, to develop a sophisticated mathematical model that simulates the motion of uranium trioxide particles under the influence of fluidizing gas. The model meticulously accounts for the interphase drag forces and the kinetic viscosity of the particulate phase. An industrial-scale denitrification fluidized bed, which includes 7 gas distribution plates, 56 nozzles, and 7.7 billion particles was modeled to investigate the impact of fluidizing gas velocity, gas inlet angle, and the diameter of the fluidizing gas inlet on the gas–solid flow characteristics within the fluidized bed. And corresponding impacts were obtained. The results show that the inlet gas flow rate is the key parameter to influence the gas–solid flow characteristics Increased inlet gas flow rate results in a lower average particle concentration, a larger amplitude of particle concentration fluctuation, more pronounced bubble disturbance effects, better fluidization, and a weaker particle aggregation effect. The research findings are crucial for optimizing the operational parameters of industrial-scale denitrification fluidized beds to ensure the highest quality of the fluidization.