The　phenomenon　of　simultaneous　nitrification　and　denitrification(SND)　has　taken　place　in　moving-bed　biofilm　reactor　(MBBR)　steadily.　The　effect　of　C/N　to　denitrification　effectiveness　has　been　also　studied　in　the　experiment.　The　results　of　the　treatment　show　that　better　denitrification　efficiency　could　be　obtained　by　increasing　C/N　ratio　and　the　removal　ratios　of　TN　reached　92.9%.　When　C/N　ratio　is　12,　the　amplitude　of　TN　removal　ratio　is　not　obvious.　The　effects　of　pH　to　ammonia　nitrogen　and　TN　removal　ratio　have　been　researched.　The　results　show　that　the　proper　range　of　pH　is　8.03-9.01　to　removing　ammonia　nitrogen　and　the　proper　range　of　pH　is　8.03-8.55　to　TN　efficiency.　The　experiment　analyzed　the　influence　of　alkalinity　and　pH　to　denitrification　efficiency,　moreover,　the　relation　of　theoretical　alkalinity　and　practical　alkalinity　has　been　studied.　The　results　indicate　that　the　influence　of　pH　and　alkalinity　to　removal　efficiency　of　ammonia　nitrogen　and　TN　is　low　in　SND,　so　does　not　need　to　adjust　pH　and　increase　alkalinity.　The　changes　of　pH　and　alkalinity　during　the　reaction　course　were　also　investigated,　and　the　result　shows　that　pH　can　indicate　the　conversion　process　of　nitrogen　during　a　single　representative　period　in　SND.