In　order　to　improve　A/O　process　denitrification　efficiency,　five　integrated　control　strategies　of　nitrate　recirculation　flow　and　external　carbon　dosage　for　denitrification　were　proposed　and　evaluated　using　the　COST/IWA　simulation　Benchmark.　Results　show　that　control　strategy　No.1　is　the　best　integrated　control　strategies　from　both　external　carbon　consumption,　effluent　quality,　and　the　stability　of　controller.　It　comprises　two　feedback　control　loops:　one　is　to　determine　the　flow　rate　of　external　carbon　source,　keeping　the　nitrate　concentration　at　the　end　of　anoxic　zone　at　a　pre-specified　level　2　mg/L,　and　the　other　is　to　adjust　the　flow　rates　of　the　nitrate　recirculation　to　keep　the　nitrate　concentration　at　the　end　of　the　aerobic　zone　at　a　pre-specified　level　based　on　the　effluent　quality　(usually　8-12　mg/L).　This　strategy　can　guarantee　highly　effective　use　of　anoxic　denitrification　capacity　in　the　low-load　condition,　and　meet　effluent　discharge　standards　through　carbon　dosage　in　the　high-load　condition.