Abstract: Based on the flow-pattern optimization of CFB boilers,the effect of bed pressure drop on combustion effi- ciency was studied. Field tests were carried out in a 480 t / h CFB boiler. The carbon content in fly ash and bottom ash under different bed pressure drops was measured and a 1-D CFB combustion model was established. Results show that the 1-D CFB combustion model can predict the effect of flow-pattern optimization on combustion efficiency. As the bed pressure drop decreases,the solid inventory in the furnace decreases and also the residence time of particles shortens. At the same time,the solid concentration in the transition zone decreases,leading to an improvement of the secondary air jet penetration. Therefore,the carbon content in fly ash always decreases with the decrease of bed pressure drop, while the carbon content in bottom ash increases. The bottom ash fraction increases with a lower bed pressure drop. The carbon loss presents a non-monotonic trend with the change of bed pressure drop. When the size distribution of feed coal particles and the bed pressure drop are adjusted reasonably,the combustion efficiency can be maintained or increased slightly after flow-pattern optimization.