Parameters　for　evaluation　criteria　of　air-water　backwashing　effects　of　a　pilot-scale　biological　aerated　filter　(BAF)　treating　petrochemical　wastewater　were　investigated.　The　parameters　included　the　suspended　solids　(SS)　and　specific　oxygen　uptake　rate　(SOUR)　of　the　backwashing　effluent,　recovery　of　the　BAF　after　backwashing,　and　the　removal　of　the　biomass/bioactivity　attached　on　the　filter　media　after　backwashing.　Results　showed　that　the　weight　of　the　total　sludge　produced　in　the　backwashing　effluent　increased　with　the　increase　in　water-backwashing　intensity,　while　the　total　SOUR　of　backwashing　effluent　rose　notably　with　the　increase　of　air-backwashing　intensity.　The　optimal　backwashing　intensity　of　14L/(m(2)s)　for　air　and　4L/(m(2)s)　for　water　were　obtained.　When　the　BAF　was　backwashed　on　this　condition,　the　BAF　recovered　with　high　average　removal　of　chemical　oxygen　demand　(COD)　and　ammonia　nitrogen　of　14.3%　and　50.3%,　respectively.　High　amount　of　biomass　removal　at　15.8%　and　low　level　of　bioactivity　removal　at　8.8%　attached　on　the　filter　media　were　also　found.　Concentrations　of　the　benzene,　toluene,　ethylbenzene　and　(o-,　m-,　p-)　xylenes　(BTEX)　and　phenol　in　the　backwashed　sludge　were　analyzed,　showing　that　the　backwashing　was　essential　to　remove　some　aromatic　compounds　adsorbed　in　the　microorganisms.