Zinc ion performed significant effect on partial nitrification. The suppression threshold on AOB bioactivity of short-term Zn (II) was 10 mg L−1. The suppression threshold on AOB bioactivity of long-term Zn (II) was 50 mg L−1. AOB in PN sludge had self-adaption and tolerance to the Zn (II). PN sludge presented profitable absorption ability for zinc ion.