Techniques　of　scanning　electron　microscopy　(SEM),　denaturing　gradient　gel　electrophoresis　(DGGE),　cloning　and　sequencing　were　utilized　together　to　study　bacterial　community　distribution　of　upper　(140-190　cm),　middle　(60-140　cm)　and　lower　(10-60　cm)　parts　of　an　up-flow　anaerobic　ammonium　oxidation　(ANAMMOX)　biofilter,　which　was　run　stably　at　low　temperature　(14.9-16.2°C).　The　results　show　that　a　large　proportion　of　ammonia　and　nitrite　proportional　disappears　in　the　middle　part　of　biofilter　and　a　high　total　nitrogen　removal　rate　of　2.4　kg/(m3·d)　is　obtained.　The　spherical　bacteria,　which　is　similar　to　ANAMMOX　bacteria,　predominates　in　the　middle　part　of　biofilter.　There　is　the　highest　bacterial　diversity　in　the　upper　part　of　biofilter,　followed　by　middle　part　and　minimum　bacterial　diversity　in　lower　part.　Bacterial　community　structures　varied　in　different　parts　of　biofilter　due　to　nitrogen　distinction　along　biofilter　layer.　There　is　only　one　type　of　ANAMMOX　bacterium　and　AOB　presented　in　different　parts　of　biofilter,　which　are　identified　as　Candidatus　Kuenenia　stuttgartiensis　and　Nitrosomonas　sp.　ENI-11,　respectively.　AOB　can　consume　trace　dissolved　oxygen　existence　in　influent,　which　is　beneficial　to　anaerobic　environment　formation　and　ANAMMOX　bacteria　enrichment　in　the　middle　part　of　biofilter.