Detection and clearance of poor fluidization in a simulated fluidized bed ash cooler were studied by analyzing the mixing properties of the bed materials and the pressure fluctuation of the air header distributor. We observed a bridge of large particles at the bed surface which caused the poor fluidization area to form at the entrance of the FBAC. The poor fluidization was caused not only by airflow rates but also by the particle discharge rates as well as particle size distribution in the FBAC. Additionally, we could easily detect the local poor fluidization through a simple method developed in the simulated FBAC and in the FBAC of the Tonghae CFB boiler. As local poor fluidization is detected, it should be possible to clear it up by regulating the now rate of each air header in the FBAC.