Abstract. The paper aims to study the fast start-up of anaerobic-aerobic-anoxic-aerobic sequencing batch reactor, with domestic sewage as treating object, to solve the problem of SBR that can be used for denitrification or dephosphorization independently and to realize simultaneous nitrogen and phosphorus removal in a single SBR system. Phosphorus accumulating organisms were enriched at the anaerobic condition for 2h/aerobic for 3h after activated sludge were inoculated. Then denitrifying polyphosphate-accumulating organisms were enriched by inserting an anoxic phase into the aerobic phase. The lengths of anaerobic time, anoxic time and aerobic time were adjusted and the nitrogen and phosphorus removal effect of (AO)2SBR system were observed. The (AO)2SBR system was started successfully with 80d of training and domesticating. The nitrogen and phosphorus removal effect was performed preferably at the condition of anaerobic(2h)-aerobic(1.5h)-anoxic(1.5h)-aerobic(0.5h). The removal rate of COD, NH4+-N, TN and TP reached 90%, 97%, 88% and 92% respectively. And 33% of energy was saved when aerobic time was shortened from 3h to 2h, while the treating effect dropped off rarely. The results show that (AO)2SBR is applicable for simultaneous nitrogen and phosphorus removal, and the effluent water quality meets the first level B criteria specified in Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant(GB 18918-2002). The system can also reach the aim of saving energy and providing theoretical basis for the nitrogen and phosphorus removal in single SBR systems.