The　relativity　between　nitrate　concentration　at　the　end　of　anoxic　zone　and　oxidation-reduction　potential　(ORP)　was　studied　by　using　starch　wastewater.　Results　show　that　the　relativity　between　them　is　very　good,　and　ORP　can　be　worked　as　nitrate　recirculation　flow　and　external　carbon　dose　on-line　fuzzy　control　parameters　respectively.　The　ORP　fuzzy　controller　was　designed.　The　controlling　nitrate　recirculation　flow　and　external　carbon　dose,　keeping　ORP　in　(-86±2)　mV　and　(-90±2)　mV,　respectively,　can　realize　A/O　process　as　the　optimal　control　for　nitrogen　removal.