The aim of this study was to investigate the denitrification performance and analyze the variation of microbial communities in immobilized particles which used in real municipal wastewater treatment. The bioreactor has achieved good denitrification effect on real municipal wastewater treatment, the NO3--N and TN removal efficiencies reached 77.4% and 68.3%, respectively. High-throughput sequencing shows that the community structure and relative abundance of bacteria changed greatly, especially at the phyla and genes levels in immobilized particles. Through the investigation of this paper, we think the influence of microflora variation should be considered when using microbial immobilized technology for wastewater treatment, and we suggest that immobilized particles cannot be used indefinitely and it needs to be replaced periodically.