Worm predation is one of the promising techniques for sludge reduction with the advantage of high efficiency and eco-friendliness. In order to achieve high quality effluent and low sludge production simultaneously, worm reactor (WR) with an efficient wastewater treatment process (anaerobic-anoxic-oxic membrane bioreactor (A(2)O-MBR)) was coupled with an auxiliary phosphorus removal reactor (PRR) to establish an A(2)O-MBR-WR-PRR combined system. In A(2)O-MBR-WR-PRR, high quality effluent with 27.7 +/- 9.3 mg/L COD, 13.0 +/- 1.8 mg/L TN and 0.4 +/- 0.2 mg/L TP was obtained, and the sludge yield was reduced by 49.8% compared with the conventional A(2)O-MBR. Besides, the roles of WR on the A(2)O-MBR-WR-PRR system were deeply investigated. In comparison with conventional A(2)O-MBR, the removal capacities of TN and TP in the wastewater treatment process were increased by 11.6% and 100.8% respectively. Further analysis suggested that in A(2)O-MBR sludge activities were improved and the functional bacteria were enriched due to the recirculation of non-consumed sludge from WR. Moreover, analysis of sludge reduction mechanisms revealed that WR led to the highest sludge reduction efficiency (41.7%) in the A(2)O-MBR-WR-PRR combined system. Meanwhile, energy uncoupling (2.3%), microbial community changes and lysis-cryptic growth (5.8%) were identified in A(2)O-MBR, which contributed to further sludge reduction. This study provided an efficient approach for practical application of worm predation for sludge reduction and wastewater treatment.