This　paper　quantifies　the　influence　of　operating　conditions　on　the　efficiency　of　domestic　wastewater　treatment　and　of　membrane　bioreactors　(MBR)　performance　with　a　statistical　method　(multivariate　linear　regression　model).　The　impact　of　the　following　seven　parameters-(1)　transmembrane　pressure　(TMP),　(2)　mixed　liquor　suspended　solids　(MLSS),　(3)　dissolved　oxygen　concentration　(DO),　(4)　hydraulic　retention　time　(HRT),　(5)　sludge　retention　time　(SRT),　(6)　temperature　(T)　and　(7)　pH　on　the　accumulated　filtrate　volume　(V)　and　water　quality　(COD,　NH3-N)　-were　investigated.　The　results　showed　that　MLSS　and　temperature　had　34%　and　about　23%　respectively　the　majority　of　the　influence　on　the　resulting　filtrate　volume　among　the　seven　influencing　parameters.　The　mathematic　expression　obtained　by　the　multivariate　linear　regression　model　between　the　accumulated　filtrate　volume　and　operating　conditions　was　V　=　249.64TMP-0.056MLSS+　31.69DO　+　55.06pH-5.25T-8.82HRT　+　16.24.　The　COD　of　the　filtrate　primarily　depended　on　the　process　temperature,　which　carried　about　64%　of　the　weight　among　all　the　seven　investigated　parameters.　The　ammonia　nitrogen　concentration　(NH3-N),　of　the　effluent　was　mainly　a　function　of　MLSS　(about　40%　influence)　and　pH　(about　27%　influence).　No　effect　of　the　TMP　on　the　filtrate　quality　was　found.　In　addition,　the　mathematic　expressions　between　COD,　NH3-N　and　operating　conditions　were　COD　=　0.0073A4LSS-5.64DO　+　2.86T　+　0.099SRT　+　2.48HRT-88.82　and　NH3-N　=　0.017MLSS-12.99DO-28.86pH　+　0.90T　+　0.13SRT　+　201.30.　These　mathematic　expressions　could　possibly　be　used　to　optimize　and　predict　the　efficiency　of　domestic　wastewater　treatment　in　bioreactor　parameters.