Abstract: In order to investigate the influence of copper ions on settleability and denitrogenation, three sequencing batch reactors (SBR) equipped with PLC system were operated by synthetic wastewater using acetate as the single carbon source. After the nitrification and denitrification process, when the system was stable, SBR 1# was operated as a control test, copper sulphate solution was dosed to SBR 2# and SBR 3# under anoxic and aerobic conditions in each cycle. The results show that the adding of Cu²⁺ under anoxic zone leads to deterioration of sludge sedimentation, but in the aerobic stage, Cu²⁺ does not cause the deterioration of sludge settling. The presence of Cu²⁺ under anoxic and aerobic conditions do not cause proliferation of filamentous bacteria. The dosing of Cu²⁺ stimulated the secretion of more extracellular polymers against the toxic effects of Cu²⁺ and inhibited the ability of microorganisms to store PHA. The presence of Cu²⁺ under anoxic condition of SBR 2# is contributed to the formation of shortcut nitrification and denitrification, but the shortcut nitrification can not be maintained by longterm dosing. The adding Cu²⁺ in the aerobic stage of SBR 3# causes the rapid loss of nitrification and denitrification.