Halophilic　activated　sludge　was　developed　by　seeding　with　sediment　of　the　estuary　to　the　sea.　During　120d　operation,　stable　short-cut　nitrification　was　achieved　in　SBRs　treating　saline　domestic　wastewater　containing　30±2g/L　salts.　Based　on　the　short-cut　nitrification　theory　of　fresh　activated　sludge,　this　study　evaluated　some　key　process　factors　possibly　contributing　to　nitrite　accumulation　such　as　pH,　free　ammonium(FA),　temperature,　dissolved　oxygen(DO)and　aeration　time.　The　results　showed　the　optimal　pH　and　salinity　of　halophilic　activated　sludge　was　7.　5-9g/L　and　10-61g/L,　respectively.　Aeration　time　and　FA　was　not　the　reasons　inducing　high　nitrite　accumulation.　Salinity　and　temperature　have　impact　on　both　the　ammonium　oxidizing　bacteria(AOB)and　the　nitrite　oxidizing　bacteria(NOB).　However,　the　activity　of　halophilic　AOB　remained　higher　than　halophilic　NOB　during　the　experiment.　Fluorescence　in　situ　hybridization(FISH)for　visualizing　nitrification　community　of　the　sediments　and　the　halophilic　activated　sludge　showed　that　AOB　was　the　dominant　nitrifiers　in　the　both　biological　systems.　The　high　nitrite　accumulation　in　halophilic　activated　sludge　may　be　owed　to　two　reasons,　one　is　that　halophilic　AOB　has　higher　substrate　degrading　rate　than　that　of　halophilic　NOB,　the　other　is　that　the　dominant　bacterial　population　is　halophilic　AOB　other　than　halophilic　NOB.