Partial　nitrification　granular　sludge　(PNGS)　treating　domestic　sewage　was　successfully　cultivated　in　a　sequencing　batch　reactor　through　shortening　settling　time　gradually　based　on　total　suspended　solids　in　the　effluent.　The　granulation　process　contained　the　washout　of　a　part　of　flocculent　sludge,　the　gathering　of　the　remaining　flocculent　sludge,　and　the　growth　of　granules.　Depending　on　the　measurement　of　extracellular　polymer　substance　(EPS),　including　polysaccharide　(PS)　and　protein　during　different　periods,　it　was　concluded　that　EPS　was　the　key　factor　for　PNGS　formation　and　PS　was　the　main　component　of　EPS　in　the　PNGS　biomass.　PS　was　mainly　from　the　secretion　of　heterotrophic　bacteria　during　endogenous　respiration　period.　The　treatment　ability　of　PNGS　was　improved　effectively　by　high　ammonia　concentration　in　a　short　time　(18d),　and　then,　PNGS　achieved　an　efficient　and　stable　partial　nitrification　for　domestic　sewage　at　20　degrees　C.　The　ammonia　removal　rate　reached　0.7kgNm(-3)d(-1),　and　the　nitrite　accumulation　rate　was　maintained　above　95%.　The　granule　structure　improved　the　partial　nitrification　process,　mainly　due　to　the　low　DO　concentration　in　the　inner　layer　of　the　granules　surface　and　the　large　amount　of　aeration　in　the　bulk　liquid.