Abstract: In order to investigate a recovery strategy for the partial nitrification (PN) activity in autotrophic nitrogen removal sludge, three reactors were adopted in this study. R1 was operated under low DO (0.30 mg/L) and high pH (7.8) conditions in a continuous membrane bioreactor; R2 was operated under low DO (0.30 mg/L) condition in a sequencing batch rector; and R3 was operated under the conditions of anoxic-high DO-low DO (0.30 mg/L) in a sequencing batch reactor. The results showed that the recovery periods for R1, R2 and R3 were 46 d, 39 d and 48 d, respectively. The ammonia oxidation rates for the three reactors were 4.99, 4.61 and 5.64 mg/(h·g), and the final concentrations of mixed liquid suspended solids were 5.43, 4.47 and 5.16 g/L, respectively. The nitrite-oxidizing bacteria were completely suppressed in all the three reactors, which was profitable for the stability of the PN reactor. The recovery in R3 took the longest time but got a best microbial activity, while R2 enabled the highest sludge concentration. Therefore, the strategy of combining pre-cultivation under anaerobic condition with membrane bioreactor under low DO condition was favorable for recovering the PN bioactivity of autotrophic nitrogen removal sludge.