Abstract: An aerated biological fluidized tank (ABFT) was used to treat phenolic wastewater with favorable treatment efficiency. As the influent phenol concentration increased from 100 mg/L to 400 mg/L, the phenol removal rate remained around 100%, and stable phenol removal was obtained at the first of four tanks. The microbial community structure and biodiversity in the ABFT reactor were examined using methods such as scanning electron microscopy (SEM), fluorescence in situ hybridization (FISH) and denaturing gradient gel electrophoresis (DGGE). The results of SEM showed that with the increase of influent phenol concentration, filamentous microorganisms gradually became the dominant species in the membrane of the ABFT stuffing. The FISH results targeting SSU rRNA revealed that most of the filamentous microorganisms in the ABFT reactor were fungi, while the PCR-DGGE results for bacterial and fungal 16S and 18S rDNA indicated that the filamentous fungi mainly belonged to Geotrichum klebahnii, although there were also some filamentous bacteria, such as Thiothrix sp. and actinobacterium. Cluster analysis and diversity analysis showed that phenol had strong selectivity on the microbial community.