The　preent　artitle　aims　to　study　the　denitrifying　alaracter　of　simultaneous　nitrification　and　denitrification　(SND).　Under　the　condition　that　C/N　ratio　was　12,　this　paper　analyzed　the　regularities　of　triple-nitrogen　and　organic　matter　degradation　in　the　process　of　simultaneous　nitrification　and　denitrification　during　a　single　representative　period,　and　studied　the　effect　of　technical　parameters　on　the　performance　of　denitrification　in　moving-bed　biofilm　reactor　(MBBR).　The　results　show　that　the　phenomenon　of　simultaneous　nitrification　and　denitrification　take　place　in　the　moving-bed　biofilm　reactor　(MBBR),　denitrification　effect　is　excellent,　and　the　removal　efficiency　of　TN　is　90%.　The　change　law　of　ρ(DO),　oxidation-reduction　potential　(ORP),　pH　and　alkalinity　during　the　reaction　course　were　investigated,　and　the　relationship　between　the　parameters　and　contaminants　was　established.　Meanwhile,　the　thesis　studied　comparatively　the　relation　between　simulation　alkalinity　and　practical　alkalinity　during　experiment.　The　results　show　that,　in　the　moving-bed　biofilm　reactor　(MBBR),　alkalinity　which　is　produced　by　effect　of　simultaneous　denitrification　can　supplement　consumptive　alkalinity　of　nitrification,　and　therefore　alkalinity　needn＇t　to　be　supplemented　in　the　process.