A novel reactor characterized by the addition and internal loop of carrier was developed and its performance was examined with synthetic domestic wastewater. The internal loop was achieved by injecting air through a gas aerator located at the reactor bottom, the aim was to produce aerobic and anoxic area in the reactor and bring about the nitrification and denitrification in a single reactor. The COD，NH4 +-N and TN removal efficiency in the reactor and the biomass change on the carrier were investigated, COD removal efficiency of 80% was achieved in three weeks after the initiation of the reactor, the biomass on the carrier peaked 7.27kg/m3 after 55 days. The reactor had a steady COD removal efficiency with an average removal rate of 80% at the influent COD range of 200-600mg/L, or at the COD volumetric load of 0.71-2.16 kgCOD/m3.d; the maximum removal of NH4 +-N and TN were 97.7% and 52.5%. The test results showed the novel reactor effectively removed TN and COD in domestic wastewater, it can realized the simultaneous nitrification and denitrification (SND) process by adjusting the macro-environment and the stratification of bioflim in a microscopic scale in the reactor