It was confirmed that the combustion action in dense bed is different between the bubbling bed and circulating fluidized bed by the measurement of the gas profile distribution and combustion fraction distribution along the furnace height. The bed quality results in the mass transfer resistance increasing, which effects the combustion reaction in dense bed. The combustion reaction in dense bed is in reduce condition. The combustion occurs all along the furnace even in the cyclone. A comprehensive model is proposed here to predict the axial gas concentration profile in the dense be, which is considered the mass transfer resistance between the solid and gas in dense bed. Calculations indicated that the resistance has a great effect on the combustion in the dense bed. Experimental data and results of the model are in good agreement.