Biodegradability of PNP has been reported widely in recent years, but the community composition of PNP-degrading microorganisms was still unclear today. In this paper, the biodegradation process with continuously PNP loading from 0 to 6.50 kg m(-3) d(-1) in 58 days in an aerobic biological fluidized bed (ABFB) reactor has been investigated. The results show that COD and PNP removal stabilized at 95% and 99% during the operation period with a maximum PNP concentration of 1250 mg/L. The high concentration of PNP in substrate led to a significant increase in extracellular polymeric substances (EPS) component of biomass and obvious morphological changes of microbial colonies during the degradation process. In addition, high-throughput sequencing was employed to reveal the highly diverse bacterial and fungal populations in the reactor. At the same time, genera Sphingobium, Penicillum and Debwyomyces belonging to phyla Proteobacteria and Ascomycota were identified to be the dominant species in high concentration PNP degradation process. This work investigated the tolerable degree of aerobic microbes to PNP toxicity as well as the characteristics of microbial communities at different PNP concentration levels. It might add some new insights into bacterial and fungal communities in high p-nitrophenol concentration degradation processes.