To　study　the　impact　of　ammonia　nitrogen　concentration　on　the　CANON　process　in　different　sludge　systems,　the　nitrogen　removal　performance　was　researched　by　the　sudden　decrease　of　the　influent　ammonia　concentration　in　the　stable　operation　of　the　granule　and　combined　floc-granule　CANON　process　at　the　temperature　of　(30±1)　and　the　pH　of　7-8.　Under　the　conditions　of　FA　concentrations　at　34,　20　and　10　mg/L,　the　short　cut　nitrification　of　the　granule　system　was　stable,　and　the　ratio　of　nitrate　increase/ammonia　consumption　was　less　than　0.11.　When　the　FA　concentration　was　33　mg/L,　the　short　cut　nitrification　operated　stably　in　the　combined　floc-granule　CANON　system.　When　the　concentration　of　FA　was　decreased　to　16　mg/L,　the　ratio　of　nitrate　increase/ammonia　consumption　was　close　to　0.11　and　the　NOB　activity　was　recovered　slightly.　When　the　concentration　of　FA　was　decreased　to　7　mg/L,　the　ratio　of　nitrate　increase/ammonia　consumption　reached　to　0.37　and　the　NOB　activity　was　fully　recovered.　The　results　show　that　the　granular　sludge　system　has　better　resistance　to　shock　loads　compared　to　the　combined　floc-granule　system,　and　the　shorter　settling　time　is　the　key　to　ensure　the　stable　operation　of　granular　sludge　system.　After　the　partial　nitrification　was　destroyed,　the　activity　of　NOB　was　effectively　inhibited　by　increasing　ammonia　concentration.　The　distribution　rule　of　sludge　size　can　be　used　to　determine　the　stability　of　the　reaction　system,　and　the　nitrogen　removal　performance　of　CANON　process　in　this　study.　The　quantitative　PCR　results　show　that,　the　abundance　of　ANAMMOX　has　obvious　decreasing　when　the　ammonia　concentration　decreased,　and　the　abundance　of　NOB　has　obvious　growth　with　the　granules　disaggregation.　©　2018,　Editorial　Board　of　Journal　of　Harbin　Institute　of　Technology.　All　right　reserved.