Nowadays the numerical simulation of a fluidized bed made of particles with a very small diameter (about a few microns) is challenging. Recently it has identified that the bad predictions of such fluidized bed come primary from an unadapted computational grids, generally too coarse. Indeed coarse grid is unable for capturing very small structures of solid appearing in such fluidized bed. But for performing numerical simulation with reasonable grid in terms cell size and, consequently, in terms of cell number it is possible to use a subgrid model for representing the effect of small structure on the large scale particle motion. In the present study we propose a posteriori test of a subgrid model for the drag in the case of 3-dimensional numerical simulation of an isothermal fluidized bed. The numerical predictions are compared with experimental pressure drop. The sensitivity with respect to the model constant is check as well as the effect of boundary condition for the solid phase. The results show that without the subgrid model all particles are entrained very quickly. In contrast, with the subgrid model, the behaviour of experimental dense fluidized bed is observed.