Abstract: An combined filler ANAMMOX (anaerobic ammonium oxidation) system was constructed to achieve the high efficient enrichment of anaerobic ammonium oxidation bacteria (AnAOB) by adding activated carbon filler on the 26^th day and composite filler on the 95^th day. The nitrogen removal efficiency of the ANAMMOX system at different operating stages was investigated, and 16S rRNA high-throughput sequencing was used to analyze the changes of microbial diversity and community structure of the sludge. The results showed that: (1) After 160 days′ operation, the composite filler ANAMMOX system was constructed successfully showed good shock load resistance. During stable operation stages, total nitrogen volumetric load (NLR) and total nitrogen removal load (NRR) of the system reached 0.97 and 0.83 kg/(m³·d), respectively. The stoichiometric ratio was close to the theoretical value of 1∶1.32∶0.26. (2) The composite filler ANAMMOX system promoted enrichment of AnAOB, and finally ANAMMOX granular sludge appeared with a large amount of AnAOB gathered on the surface of the composite filler to form a red biofilm. (3) On the 160^th day, the system was dominated by AnAOB. Phylum level analysis revealed that the relative abundance of the Planctomycetotes increased from 0.77% to 33.17%, the relative abundance of Chloroflexi increased from 9.17% to 22.65%, while the relative abundance of other phylum decreased. In addition, the relative abundance of Candidatus jettenia and Candidatus brocadia on genus level increased to 30.56% and 1.93%, respectively. The study indicated that the combined filler ANAMMOX system is beneficial to achieve high-efficient enrichment of AnAOB and maintain the stable nitrogen removal efficiency.