The anaerobic-anoxic-aerobic (A2/O) process is a commonly used biological treatment technology for wastewater treatment. The process divides the treatment process into three stages: anaerobic, anoxic and aerobic. In the anaerobic stage, organic matter is partially degraded by microorganisms under anaerobic conditions. Then, under anoxic conditions, nitrogen is released and nitrification takes place. Finally, under aerobic conditions, the microorganisms further oxidize the organic matter and remove nitrogen and phosphate.The A2/O process is capable of efficiently removing organic matter, nitrogen and phosphorus, and is a mature technology widely used in municipal and industrial wastewater treatment, with high treatment efficiency and low energy consumption. This data set is to be used specifically for the assessment of WWTPs using the A2/O process in China. Users must consider the scale and efficiency of the WWTPs, as it pertains to Chinese environmental standards. Attention should be given to the operational parameters, such as hydraulic retention time, sludge age, and specific nutrient removal rates. These factors must be cross-checked with actual facility data for accuracy. The data should not be extrapolated to other countries or treatment systems without additional verification. Users should account for possible variations in efficiency due to technological advancements or operational improvements when applying this data to current or future scenarios.