The force characteristic of the large immersed particle in the dense gas–solid fluidized bed is the significant foundation to study the kinetic behavior of the large particle. We designed three steel balls with the density of 7500 kg/m³ and the mean diameters of 8 mm, 10 mm, and 12 mm as the basic investigated objects. The coarse-sand particles and fine-glass powders were employed as different types of fluidized mediums. We used the self-designed measurement system to measure the force values of different steel balls with variable gas velocities, and the fluctuation characteristic of the forces was obtained finally. The experimental measurement results indicate that the force fluctuation of the large immersed particle with different diameters basically keeps stable after achieving the complete fluidization of the gas–solid fluidized bed. Meanwhile, the results show that the force fluctuation of the same large immersed particle is more stable when the coarse-sand particles are selected as the fluidized medium. The approach of theoretical calculation and numerical simulation has been combined to validate the reliability of measurement results. The comparison conclusions indicate that the measurement results agree well with the calculation and simulation results.