The experiment was to explore the effect of different SRT on the nitrogen removal efficiency and kinetic characteristics of AnAOB by studying the variation of nitrite removal loads (N_r), nitrite sludge loads (N_s) and kinetic characteristics with gradient decrease of SRT in a SBR. The results showed that with SRT decreasing from 21 d to 12 d, N_r decreased from 0.590 kg/(m³·d) to 0.493 kg/(m³·d) while N_s increased from 0.178 kg/(kg·d) to 0.297 kg/(kg·d), and the N-removal performance of the whole system was reduced but the N-removal efficiency of unit mass of AnAOB was significantly improved. The Monod model can well simulate the kinetic behavior of AnAOB at different SRT. The maximum specific degradation rate (v_max) increased from 0.406 d^-1 to 0.826 d^-1 and the semi-saturated constant (K_s) increased from 23.3 mg/L to 95.3 mg/L, which indicated that gradiently decreasing SRT can screen and purify AnAOB with faster grow rate, while the affinity for the substrate gradually deteriorated and the stability decreased.