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Anaerobic activated sludge plays a key role in the anaerobic digestion (AD) treatment of wastewater. The ability of anaerobic activated sludge to endure stress shock determines the performance of AD. In this study, the resistance of anaerobic activated sludge acclimated by three feeding patterns (continuous, semi-continuous, and pulse) to four stress shocks, including low pH influent, high OLR (organic loading rate), high ammonium and high sulfate, was investigated respectively. The results showed that the anaerobic activated sludge acclimated by semi-continuous feeding had the best resistance to high OLR shock, followed by pulse feeding, and then continuous feeding. There was no significant difference in the resistance of the three activated sludge to the other stress shocks. Under stress shock, the microbial community structure and abundance of specific functional microorganisms in the activated sludge acclimated by different feeding patterns varied, while the relative abundance of Methanosarcinaceae in the anaerobic activated sludge increased. The variation in the relative abundance of specific functional microorganisms was in charge of the differences in the resistance of anaerobic activated sludge. Overall, the results presented herein provide reference for improving the stability and effectiveness of activated sludge under adverse conditions. HIGHLIGHTS Resistance of activated sludge acclimated by three feeding patterns was studied.; Acclimated activated sludge was well resistant to low pH influent and high sulfate.; Sludge acclimated by semi-continuous feeding can best resist to high OLR shock.; The relative abundance of Methanosarcinaceae increased under stress shock.; Differences in functional microbial abundance led to different resistance of sludge.;