Key　operational　parameters　of　single-stage　partial　nitritation/anammox　(PN/A)　process　was　investigated　to　achieve　higher　nitrogen　removal　rate　(NRR)　and　robustness　by　using　a　sequencing　batch　reactor　(SBR)　(120L)　treating　ammonia-rich　wastewater.　Long-term　operation　demonstrated　that　the　maximum　NRR　of　the　reactor　was　1.1　kgN/(m3·d).　The　main　parameters　influenced　the　stability　of　the　reactor　were:　free　ammonia　concentration,　dissolved　oxygen　(DO)　concentration　and　the　relative　proportions　of　the　granules　and　flocs.　The　balance　of　AOB　and　anammox　activity　was　the　key　to　a　robust　single-stage　PN/A　operation.　Excess　discharge　of　floc　sludge　led　to　a　decrease　of　ammonia　oxidation　rate　and　a　high　and　inhibitory　DO　level　to　anammox　bacteria,　which　eventually　triggered　the　dramatic　drop　of　NRR.　The　limiting　factors　of　further　improvement　of　NRR　were:　(1)　sludge　concentration　stabilized　due　to　biomass　washout;　(2)　anammox　and　AOB　activity　could　not　be　promoted　simultaneously　when　further　increasing　DO　levels;　(3)　mass　transfer　could　not　be　further　enhanced.　Furthermore,　NRR　showed　strong　correlation　with　aeration　rate　in　this　study.　Therefore,　aeration　rate　could　be　an　alternative　regulating　parameter　under　fluctuating　influent　load.　©　2016,　Chinese　Society　for　Environmental　Sciences.　All　right　reserved.