A　two-step　nitrification　model　was　built　by　simplifying　the　standard　activated　sludge　model　No.　1,　and　dynamic　dissolved　oxygen　(DO)　simulation　can　be　done　for　aerobic　nitrification　process　in　a　sequencing　batch　reactor　(SBR)　with　constant　aeration　intensity.　The　parameters　in　the　model　could　be　distinguished　into　two　groups　by　model　identification:　in　a　group　parameter　values　can　be　directly　obtained,　including　yield　coefficient,　DO　saturation　coefficient　(or　substrate　coefficient),　and　in　other　group　parameter　values　needed　to　be　estimated　by　optimization　algorithm.　Adopting　the　parameter　values　recommended　by　literatures,　dynamic　processes　were　simulated　for　important　process　variables,　which　revealed　multi-DO　levels　and　fitted　well　with　the　real　response　trend　in　SBR　operation.　Optimal　experimental　design　method　was　employed　for　obtaining　dynamic　DO　data　of　aerobic　nitrification　process　in　the　SBR　with　typical　aeration　intensity,　from　which　the　values　of　KLa　and　SOeq　could　be　determined　by　theoretical　analysis　and　second　order　differential　treatment　of　these　data.　Then,　further　parameter　estimation　could　be　optimal　based　on　the　model　identification　and　KLa　determination.　©　All　Rights　Reserved.