Abstract: To facilitate the rapid start-up of the anaerobic ammonium oxidation (ANAMMOX) process and the enrichment of anaerobic ammonium-oxidizing bacteria (AnAOB), a composite carrier of nano-zero-valent iron-modified graphene oxide (nZVI@GO) was prepared via the sodium borohydride reduction method. Three different ANAMMOX reactors were set up: a blank control group (R1), a graphene oxide addition groupa (R2), and an nZVI@GO addition group (R3). The concentrations of \mathrmNH_4^+ -N (10-50 mg/L) and \mathrmNO_2^- -N (13.2-66 mg/L) in the influent water were gradually increased during the 100-day operation. The carrier surface characteristics, start-up and denitrification effects, sludge morphological changes, and the differences in microbial community structure of ANAMMOX were analyzed. The results indicated that: (1) nZVI was successfully loaded onto the graphene oxide (GO) surface, and the modified carrier exhibited a three-dimensional rough structure that provided more attachment sites for AnAOB, Additionally, Fe⁰ coexisted with Fe²⁺ and Fe³⁺ on the modified carrier. (2) The R3 device starts the fastest when the substrate concentration increases at each stage, and the \mathrmNO_2^- -N removal rate reaches 90% in a shorter time than R1 and R2. From day 81 to day 100, the removal efficiencies of \mathrmNH_4^+ -N, \mathrmNO_2^- -N and TN hit 80%, 90% and 78% respectively, and the stoichiometric proportion (Δ\mathrmNH_4^+ -N/Δ\mathrmNO_2^- -N/Δ\mathrmNO_3^- -N) approached the theoretical ratio of 1∶1.32∶0.26. (3)The sludge in R3 shifted gradually from its original black color to a reddish-brown hue, appearing more red than that in R2, indicating cytochrome C accumulation and enhanced AnAOB activity. (4) High-throughput sequencing of the inoculated sludge and sludge on day 60 of operation revealed that the relative abundance of Planctomycetes, the phylum to which AnAOB belonged, increased by 4.22, 3.72, and 10.93 percentage points in R1, R2, and R3, respectively. At the genus level, the predominant AnAOB genus in all three devices was Candidatus_Jettenia, with relative abundance increases of 3.25, 3.04, and 13.61 percentage points in R1, R2, and R3, respectively. The study demonstrates that nZVI@GO significantly promotes AnAOB enrichment and exhibits better stability.