In　this　research,　the　removal　efficiency　of　As(III)　by　biofilter　was　studied　under　filtration　velocity　of　3,　4　and　5　m/h　respectively,　using　well-established　biofilter　column　and　synthetic　raw　water　which　contains　As(III),　Fe(II)　and　Mn(II)　in　the　concentration　of　30-200　μg/L,　0.5-1.5　mg/L　and　0.6-2.0　mg/L,　respectively.　The　results　indicate　that　the　removal　efficiency　of　biofilter　on　As(III)　can　be　over　95%,　and　it　is　not　affected　by　As　with　the　concentration　below　200　μg/L　in　the　raw　water.　The　capability　of　arsenic　removal　of　the　biofilter　is　found　to　concentrate　in　the　filter　bed　with　deepness　of　0-660　mm　after　measuring　the　samples　from　different　sampling　places.　And　As(III)and　Fe(II)　will　exceed　the　standards　for　a　short　time　after　back-washing.