Abstract: The dynamic model of a pressurized fluidized bed combustor was studied. In order to reflect the distribution of temperature along the axial direction as well as to increase the speed of model calculation, a combined discretization strategy was applied, which divided the combustor into a certain number of cells for hydrodynamic and heat transfer calculations and further grouped some neighboring cells into a smaller number of sections for mass and energy balance calculations. By dividing the dense bed into three different phases and considering the bubble behavior and gas mass transfer between the adjacent phases, the model was able to simulate the bypassing of oxygen from bottom to the freeboard as well as the difference of oxygen concentration in different phases. The dynamic model was set up based on the dynamic balance equations of solid mass, oxygen mass, carbon mass and total energy in each section. The static balance calculation results of the model were compared with the experimental data from a real 60 t·h ^-1 PFBC boiler and agreement was found to some extent. Finally, the fast bottom ash draining process was simulated with the model, which showed that the model indeed had the ability to describe this unique load changing operation of PFBC correctly and reflected the combustion mechanism of fluidized bed essentially.