on N/VSS, which was 2.9 and 3.9 times that of the sludge activity before phosphorus addition, respectively. The bacterial community structure illustrated that the denitrifiers increased remarkably from 13.47% to 44.82% and that the dominate bacteria have also changed. Meanwhile, the growth of autotrophic, heterotrophic, and mixtrophic bacteria were all improved significantly after phosphorus was added.