The experiments were conducted to research biofilter' s purifying ability .Several water quality indexes were tested in Eriocheir sinenisis' s larvae rearing pond to know the treatment effect .Compared with other treatment methods in traditional breeding , biofilter is more efficient in water purification .The removal rate of COD was 55 .5 %, the removal rate of ammonia-N was 33 .2 %. During the breeding process , pH was stable and DO was abundant .There were no DO debt and stink in rearing pond .