Raw　water　samples　were　taken　in　bench　scale,　using　AOB　as　target　microorganism.　The　study　investigated　the　oxidation　efficiency　of　two　oxidants　to　AOB　by　compared　monochloramine　(NH2Cl),　chlorine　dioxide　(ClO2)　with　the　combination.　Berenbaum　formula　was　introduced　to　judge　the　synergistic　nature　of　the　combined　oxidants,　and　this　article　also　studied　the　biological　safety　of　filtration　effluent　oxidized　by　the　combination　of　NH2Cl　and　ClO2.　Results　showed　that　there　was　certain　efficiency　when　using　NH2Cl　or　ClO2,　respectively.　When　AOB　was　inactivated　to　a　logarithmic　level　of　5.26,　1.5　mg/L　chlorine　needed　30　minutes,　while　0.225　mg/L　chlorine　dioxide　only　needed　15　minutes.　It　was　demonstrated　that　to　get　the　same　inactivation　rate　of　AOB,　ClO2　needed　lower　oxidation　dosage　and　shorter　contact　time　when　compared　to　NH2Cl.　Compared　with　the　individual　oxidantion　of　NH2Cl　or　ClO2,　NH2Cl　combined　with　ClO2　had　better　oxidation　efficiency　to　AOB.　According　to　the　Berenbaum　formula,　the　combination　of　NH2Cl　and　ClO2　was　synergistic　to　AOB.　Oxidation　experiment　was　also　carried　on　simulative　filtration　effluent　samples,　results　showed　that　the　residual　of　ClO2　was　increased　obviously　resulted　from　the　exit　of　NH2Cl,　which　could　prevent　bacteria　regrowth　in　distribution.　Therefore,　the　combined　oxidants　of　NH2Cl　and　ClO2　were　better　than　NH2Cl　or　ClO2　since　the　oxidant　dosage　and　byproducts　were　significantly　decreased,　followed　by　safer　biclogical　stability.