Wastewater　treatment　plant　control　and　monitoring　can　help　to　achieve　good　effluent　quality,　in　a　complex,　highly　non-linear　process.　This　paper　presents　the　A/O　biological　Nitrogen　Removal　Simulator　based　on　ASM3.　Steady　state　simulation　and　kinetic　simulation　were　carried　out　with　the　simulator.　The　results　show　that　the　overall　tendency　of　COD,　NH(3)-N　and　NO(3)(-)-N　simulated　value　and　measured　value　almost　consistent　in　both　the　steady　state　simulation　and　kinetic　simulation.　The　relative　error　of　the　simulator　that　based　on　ASM3　is　within　the　range　that　can　be　accepted.　So　the　results　confirmed　the　validity　and　practicability　of　the　simulator.