Landfill　leachate　is　treated　by　two-stage　UASB-A/O　process.　Batch　tests　were　conducted　with　the　activated　sludge　taken　from　A/O　reactor,　which　is　of　good　properties　of　biological　nitrogen　removal.　The　impacts　of　salinity　shocks　on　SOUR,　ammonia　oxidation　rate,　and　nitrite　accumulation　rate　of　different　microorganisms,　as　well　as　profile　of　pH,　are　investigated,　especially,　its　effect　on　N2O　production　during　nitrite　denitrification.　The　results　show　that　the　order　of　inhibition　strength　by　salinity　is　follows:　NOB　＞　AOB　＞　carbon　oxidation　bacteria;　while　the　reaction　for　salinity　shocks:　carbon-oxidizing　bacteria　and　NOB　are　better　than　AOB.　For　all　microorganisms　tested,　the　ammonia　oxidation　rate　decrease　gradually　with　increase　of　salinity,　but　the　reduction　level　is　quite　different.　At　the　same　concentration　of　initial　ammonia,　nitrite　accumulation　rate　goes　slightly　up　with　the　increase　of　salinity,　from　93.1%　at　5　g　·　L-1　salt　to　98.6%　at　35　g　·　L-1　salt.　The　curve　of　pH　can　be　used　as　on-line　control　parameters,　indicating　the　end　of　short-nitrification　and　short-denitrification　by　salinity　shock.　The　delay　of　nitrite　denitrification　and　the　increase　of　N2O　peak　concentration　would　appear　during　the　process　of　salinity　shock.