Air and particle motions in a bubbling fluidized bed of 310 gm. glass beads, which were classified as B particles in the Geldart map, were numerically simulated. The two-dimensional Navier-Stokes equations for the air motion and the Lagrangian equations for the particle motion were simultaneously solved by taking into account the multi-body collisions among particles calculated using DEM and the mutual interaction between the air and the particles based on the drag and the lift forces. Comparison of the calculated and the experimental results showed that the calculated results represent well the real particle and air motions in the bubbling fluidized bed and clarify the mechanism of the various bubble dynamics, for example, bubble formation, coalescence and disruption in the bubbling fluidized bed. It was also found that the very high air fluctuating kinetic energy in the fluidized bed was mainly yielded by the pressure gradient velocity correlations and dissipated by the air particle interactions. Then the expression of the pressure term for the continuum model of the particle phase in the fluidized bed is the most important matter.