In this paper, porous alumina was used as an alternative bed material to reduce polycyclic aromatic hydrocarbon (PAH) emission and improve the combustion efficiency during sewage sludge combustion in a fluidized bed combustor (FBC). To discover the reduction mechanism, the Brunauer-Emmett-Teller (BET) surface area, critical fluidized velocity, and heat-transfer coefficient of three bed materials (silica sand, alumina sand, and porous alumina sand) were characterized. In comparison to the conventional silica bed material, the reduction efficiencies of PAH emission and PAH total toxic equivalent (TEQ) by porous alumina bed material under 850 degrees C were 52.0 and 97.7%, respectively. Porous alumina bed material had more BET surface area than that of the conventional silica sand, which could adsorb gaseous hydrocarbon and prolong the residence time of hydrocarbon in the diluted zone of the FBC. At the same time, it was well-known that gaseous hydrocarbons were a precursor of PAHs. Thus, PAH formation was suppressed. Moreover, the low heat-transfer coefficient would decrease the heat transmission rate between the bed materials and sewage sludge, which caused the sewage sludge decomposition rate in porous alumina bed material to be lower than that of silica bed material. Hence, less gaseous hydrocarbons and PAHs were formed. In addition, alumina bed material may inhibit agglomeration and enhance the fluidization quality of a fluidized bed incinerator. The above mechanism may account for reducing PAH formation by porous alumina bed material.