Abstract: The anaerobic ammonium oxidation (ANAMMOX) process is a new biochemical removal process with a low demand of energy and costs. However, the slow growth rate and high sensibility of ANAMMOX bacteria caused long set-up time and unstable operation. Three UAFB-ANAMMOX reactors with different carriers (i.e., combined carrier, polyurethane foam, elastic fiber) were set-up with the artificial water. The biofilm formation and nitrogen removal efficiency of ANAMMOX in three reactors were investigated. The results showed that, compared with the polyurethane foam and elastic fiber, the reactor 1with combined carrier had shorter set-up time (42d) and more stable performance. In the last stage, NH₄⁺-N and NO₂^--N removal efficiencies both reached up to 90%, and the maximum NLRs was 1.239kg/(m³·d). The biofilm connected with the combined carrier were closely and uneven. However, the biofilm on polyurethane foam were incompact and easy to washing off. The set-up time of reactor 2with polyurethane foam was 66d. The NH₄⁺-N and NO₂^--N removal efficiency in reactor 2were more than 90% and 95%, and the maximum NLRs was 1.268kg/(m³·d). Reactor 3with elastic fiber was not stable and sensitive to dissolved oxygen, substrate concentration and hydraulic impact, and the maximum NLRs was only 0.724kg/(m³·d).