The dynamic behavior of a screen packed fluidized bed combustor of 6.7cm inside diameter was investigated by the residence time distribution and the temperature profile of combustion. The low grade anthracite coal(H.V.<3000kcal/kg) of uniform size was used in this experiment and the thermal analysis was performed in order to know the combustion characteristics of coal particles. Considering the dynamic behavior of the packed fluidized be combustor, a combustion model which was consisted of a mixed zone and a dispersed zone of particles was proposed. It was found from the model that the particle mixing, which was caused by the counter-current flow of particles was influenced by the heating value of coal and that a packed fluidized be was more effective for the combustion of low grade anthracite coal having high segregation effect of burning particles.