Abstract: The dephosphorization-nitrosation for two ways of discharging sludge in three different gradients of SRT( 40,20,10 d) were studied with an SBR which treated domestic wastewater at normal temperature( 20- 25 ℃). The results show that,with the decrease of SRT,the dephosphorization improves gradually and the volumetric load of ammonia removal reduces gradually. In the same condition of SRT,discharging sludge from the top of the sludge bed get a better phosphorus removal and higher volumetric load of ammonia removal than that from the bottom. In the long run, the stable operation of dephosphorization-nitrosation treating domestic wastewater by SBR at normal temperature was achieved by discharging sludge from the top of the sludge bed and controlling the sludge age at 20 d. In this condition,the effluent concentration of TP was 0.1-0.4 mg/L,TP removal rate was 95.92%-97.12%,the volumetricload of ammonium removal was 0.12 kg/( m³·d) and the ratio of nitrite nitrogen and ammonia nitrogen in the effluent was about 1∶ 1,which provided the appropriate inlet for anaerobic ammonia oxidation.