An innovative hydrodynamic parameter, specific energy dissipation rate (omega), is proposed and defined as the energy dissipation at the biofilm surface (by erosive effect of flowing water surrounding the bioparticle) per unit volume of fluidized-bed bioreactor per unit time. From the simulated results, omega is varied with operating flow rate and bed expansion characteristics. The biofilm thickness (delta) is found to be inversely proportional to omega. A small omega value benefits the growth of a thick biofilm. Thus, at different stages (e.g., during start-up and at different biofilm thicknesses) the model can be applied to predetermine a better operating scheme. The experimental results also show that the steady-state biofilm thickness measured in the upper and lower parts of the bioreactors is inversely proportional to omega values. Biofilm thickness and omega in the upper part of the bioreactors are respectively larger and smaller than those in the lower part. In addition, by referring to the published data, delta correlates well with omega, and thus the proposed model is well verified.